Unit 1 · Scarcity, Choice and Opportunity Cost

Picture a $40 gift card to a store you like. You walk in wanting headphones at $35, a hoodie at $30 and sneakers at $60. Your wants add up to $125 and the card holds $40. Now imagine a relative hands you a second card worth $200. You can buy all three items, but on the way to the register you notice concert tickets at $90 and a jacket at $120. The list of things you want did not close. It grew to fit the new money.

That is scarcity: the condition in which people want more than the available resources can provide. Scarcity is not the same as being poor. A student with $40 and a company with $40 billion both face it, because wants expand faster than means. Time makes the point most clearly. Every person on Earth, rich or poor, gets the same 24 hours a day, and almost everyone wants more from those hours than they can hold.

Economics is the study of how people choose to use scarce resources to satisfy their wants. Economists study those choices at two scales. Microeconomics looks at individual households, businesses and markets, such as how a bakery sets its prices. Macroeconomics looks at the whole economy, such as why unemployment rises in a recession. This unit begins where all of it begins, with the fact that choices must be made.

The most important consequence of scarcity is choice. Because you cannot have everything, picking one thing means not picking another. Maya could not fit the movie and nine hours of sleep into the same night. A city cannot put the same $200,000 into both a park and a fire truck. The next chapter measures exactly what a choice costs. This chapter asks a bigger question first: since everyone must choose, who decides, and how?

A popular game console launches at $500 in November. Stores sell out in hours, and people who wanted one walk away empty-handed. Twelve weeks later the same console sits on the shelf at the same $500, and anyone who wants one can buy it. In November there was a shortage: at the going price, the quantity demanded by buyers was larger than the quantity supplied by sellers. By February the shortage was gone.

Put numbers on it. Suppose that at $500, buyers wanted 1,000,000 consoles in launch week, but the maker could ship only 600,000. The shortage was 1,000,000 minus 600,000, or 400,000 consoles. By week twelve the factories had caught up and shipped 1,000,000, so quantity supplied matched quantity demanded. A shortage ends when supply catches up or when the price rises enough that fewer people want to buy.

Scarcity did not end in February. The console was still scarce, because making each one used up chips, plastic, factory time and workers that could have made something else. Here is the test: if the price were zero, would people want more of it than exists? For consoles, yes. For almost everything, yes. Scarcity is the permanent gap between wants and resources. A shortage is a temporary gap between what buyers want and what sellers offer at one particular price.

The difference matters because the two problems have different fixes. A shortage can be fixed by producing more or by letting the price rise. Scarcity cannot be fixed at all; it can only be managed by choosing well. Watch the news for the word shortage. A drought that cuts a town’s water supply creates a real shortage at the current water rates. But water was scarce before the drought and will be scarce in a wet year too, because it is never free to collect, clean and deliver.

A club at school offers free pizza at its Thursday meeting. To you the price is zero. Look closer. The club paid $60 out of its dues. The pizza shop used flour, cheese, an oven and a worker’s time. You spent thirty minutes in a room you might have spent somewhere else. The pizza was free to you, but it was not free. Someone paid in money, and everyone paid in resources that could have gone to another use.

Economists sort goods into two piles. A free good is one that exists in greater quantity than people want even at a price of zero, so nobody has to give anything up to get more of it. Sunlight on a farm field and the air you breathe outdoors are the standard examples. An economic good is scarce: getting more of it requires giving something up. Nearly everything you can name, from pencils to public schools, is an economic good. Illinois spends thousands of dollars per student each year to run its public schools, all of it raised through taxes.

Try it with numbers. A city announces that it will give away 5,000 free shade trees to residents. Each tree costs $40 to grow, deliver and plant. The program costs 5,000 times $40, or $200,000, paid from the city budget. That $200,000 is not available for road repair, library hours or a tax cut. The trees may be a wonderful use of the money. They are still not free. The cost simply landed somewhere other than the person taking the tree home.

Asking who really pays, and what was given up, is the first habit of economic thinking. It does not mean free lunches are bad. Free school meals, free concerts in Millennium Park and free clinics can be worth every dollar. It means the dollars exist and came from somewhere. When a program is called free, an economist hears a question: free to whom, and paid for by whom?

Follow a loaf of bread backward from a Chicago bakery. The flour came from wheat that grew in soil, drank rain and soaked up sunlight. A farmer planted and harvested it, a mill ground it, a truck driver hauled it, and a baker mixed and shaped it before dawn. Economists group everything used to make the loaf into four categories called the factors of production: land, labor, capital and entrepreneurship. This lesson covers the first two.

Land means every natural resource, not just dirt. It includes soil, water, minerals, timber, oil, wind and the fish in Lake Michigan. Illinois is rich in this factor. Its deep prairie soil is among the most productive in the world, and the state is one of the nation’s leading producers of corn and soybeans. Land earns a payment called rent. A landowner who lets a farmer use 100 acres is renting out a factor of production.

Labor means human effort, both physical and mental. The farmer, the truck driver, the baker, a nurse, a software developer and a teacher are all supplying labor. Its payment is wages. Labor has quantity, meaning workers times hours, and quality. The quality part is called human capital: the skills, knowledge and health a worker brings to the job. Two bakers can share the same oven, yet a trained baker turns out 80 loaves in a shift while a beginner turns out 50. That extra 30 loaves is a 60 percent gain, and it came entirely from human capital.

Countries and regions differ in which factors they have. Illinois has abundant farmland and a large, skilled workforce clustered around Chicago. A small island nation may have little land but plenty of labor. Economists ask which factor is scarce in a place, because that shapes what the place produces and what it trades for. A region does not need to have every factor. It needs to use the ones it has well.

Back in the bakery, look at what the baker uses: an oven, two mixers, a walk-in cooler, a delivery van and the building itself. Economists call these capital: goods that were produced in order to produce other goods and services. Here is a common mistake. In everyday talk, capital means money. In economics, the $6,000 the baker spent is not capital; the mixer she bought with it is. Money buys factors of production, but money itself bakes nothing.

Capital matters because it raises productivity, the amount of output a worker produces in an hour. Suppose the baker kneads by hand and makes 40 loaves a day. She buys a $6,000 mixer and now makes 120 loaves a day with the same hours. Output tripled, a rise of 200 percent. Notice that the mixer was itself made from steel, wire and labor. Someone had to give up making consumer goods to make that machine. A society builds capital by saving, which means not consuming everything it produces today.

The fourth factor is the person who put the bakery together. An entrepreneur has an idea, gathers land, labor and capital, and takes the risk that the idea will fail. The baker signed a lease, borrowed $6,000, hired two workers and opened the doors without knowing whether anyone would buy her bread. If they do not, she loses her savings. If they do, she earns profit, the money left after all costs are paid. Profit is the reward for taking that risk, and the chance of loss is what makes it a risk.

Put the four factors together with the payment each one earns. Land earns rent. Labor earns wages. Capital earns interest, the payment for the use of saved money and the machines it buys. Entrepreneurship earns profit. Every business on every block in Chicago, from a corner taqueria to a steel plant, combines these four. How much of each a country has, and how well it combines them, decides how much that country can produce.

Stand on one acre of Illinois farmland. In the 1930s that acre produced roughly 30 bushels of corn in a good year. Today the same acre often produces close to 200. The soil did not get bigger. What changed was everything applied to it: hybrid seed, tractors and combines, fertilizer, drainage, weather data and three generations of farming knowledge. Those are capital, human capital and technology, and together they multiplied what one acre can do.

This is productivity at work. Productivity is output per unit of input, usually measured per worker per hour or per acre. Compare two sandwich stations in a cafe. At station A a worker makes 12 sandwiches an hour. At station B, with a better layout and a faster press, a worker makes 20. With two workers on eight-hour shifts, station A yields 2 times 8 times 12, or 192 sandwiches a day. Station B yields 2 times 8 times 20, or 320. Same workers, same hours, 128 more sandwiches.

Where does higher productivity come from? From more and better capital, from human capital built by education and training, from technology, meaning better knowledge of how to combine inputs, and from specialization, which the next chapter explains. Each source has a price. Building the better sandwich station means spending money now that could have bought other things. That is investment: giving up some consumption today to produce more tomorrow.

Over decades, productivity growth is the main reason a country’s standard of living rises. When each hour of work produces more, there is more to go around, whether it is paid out as higher wages, lower prices or more free time. A common mistake is to confuse productivity with effort. Working longer hours at the same pace raises total output but not productivity. Working with better tools, skills and methods raises both.

A high school receives a $50,000 grant. The principal faces three decisions in a row. First, what should the money become: 250 laptops at $200 each, or a new weight room? Second, how should the work be done: hire an outside contractor or have the district’s own staff install everything? Third, if it is laptops, who gets them: seniors first, one per classroom, or a lottery? Every economy, from a village to the United States, must answer those same three questions.

The first question is what to produce. Resources that go into one good cannot go into another, so a society must decide how much food, housing, health care, entertainment and defense it will make. The second is how to produce it. A field can be harvested by 40 workers with hand tools or by one worker with a combine. A car can be welded by people or by robots. Each method uses a different mix of the factors of production.

The third question is for whom. Once goods exist, some rule decides their distribution, meaning who ends up with them. Goods can go to whoever pays the most, to whoever waits in line longest, to whoever the government chooses, to whoever is related to the right people, or to everyone equally. Each rule rewards different behavior and feels fair to different people. This is the question where economics meets values most directly.

The way a society organizes its answers is its economic system. Some societies answer by custom, doing what their grandparents did. Some answer through a central authority that gives orders. Some answer through millions of separate buyers and sellers who never meet, guided by prices. Almost every real country mixes these. The next two lessons walk through each system, what it does well and what it does badly.

In a traditional economy, the three questions are answered the way they were answered last year and the century before. A family farms because its parents farmed, plants the same crops, and shares the harvest by rules of kinship and custom. Everyone knows their role, and there are few surprises. The costs are just as clear. Output stays low, new ideas are slow to spread, and a bad harvest can be a disaster. Pure traditional economies are rare today, but custom still shapes some choices in every society.

In a command economy, a central authority, usually the government, owns most of the factors of production and decides what, how and for whom. The Soviet Union ran on central planning for most of the twentieth century. Planners in Moscow set targets in five-year plans, such as a certain number of tons of steel or pairs of shoes, and factories were ordered to meet them. Prices were set by decree rather than by buyers and sellers.

Command systems have a real strength: they can point a whole nation’s resources at one goal quickly, as in wartime. Their weaknesses show up in daily life. Imagine a planner who must order shoes for 1,000,000 people. He knows the average foot is size 9, so he orders 1,000,000 pairs of size 9. People with size 7 feet line up for hours and go home empty-handed while size 9 piles up in warehouses. No planner can know what millions of people want, and a set price cannot signal when he guesses wrong. Workers and managers who are paid the same whether the shoes fit or not have little reason to fix it.

Today only a few countries, such as North Korea, come close to a pure command economy. Cuba keeps much of its economy under state control. China combines strong state direction of major industries with markets in much of daily life. Every economy that has tried to plan everything from the center has run into the same two problems: not enough information and not enough incentive. The next lesson turns to the system that tries to solve both.

Nobody in Chicago planned how many pizzas the city would make tonight. No office assigned the cheese, scheduled the drivers or decided which neighborhoods get deep dish. Yet tonight there will be pizza almost everywhere it is wanted, at prices people will pay. That is a market economy: households and businesses that own their own property make their own choices, trade with each other voluntarily, and are coordinated by prices rather than by orders.

Prices do the coordinating. Suppose a new pizza topping becomes popular and shops that offer it can charge $16 instead of $14 a pie. The higher price is a signal that people want more, and an incentive to supply it. More shops add the topping, suppliers grow more of the ingredient, and the price settles back. Adam Smith described this in 1776 as an invisible hand: each person seeks their own gain, and the result is goods reaching the people who want them, without anyone directing the whole. The system rests on private property, voluntary exchange, competition and the profit motive.

No country runs on markets alone. The United States is a mixed economy. Private businesses produce most goods and services, but government at every level builds roads, runs public schools, operates courts and the military, regulates food and drug safety, and collects taxes to pay for it all. Government spending at all levels in the United States adds up to roughly a third of the economy’s output. Illinois runs public universities and the tollway system while private firms run nearly everything else. Countries differ in the mix, from more market-based to more government-directed, but every one is somewhere in between.

Markets have clear strengths: they use dispersed information, reward efficiency and drive innovation. They also have limits that later chapters examine, including pollution that no price captures, goods like national defense that no business can sell, and periods of high unemployment. Economists broadly agree that markets do most things well. They disagree, often sharply, about how much government should do around the edges. Both the agreement and the disagreement are part of the subject.

A coffee shop near a high school starts a punch card: buy nine drinks, get the tenth free. Within a month a typical regular goes from two visits a week to three, a 50 percent increase. Across town a library charges 25 cents a day for late books, and more books come back on time. The punch card is a positive incentive, a reward for doing something. The fine is a negative incentive, a penalty for doing something. Both changed behavior without anyone giving an order.

Incentives come in many forms: money, time, grades, praise, convenience, the fear of a penalty. Prices are incentives, which is why markets work. Taxes and subsidies are incentives that governments design on purpose. A subsidy is a payment that lowers the cost of doing something, such as a tax credit for installing solar panels. A tax raises the cost. In 2017 Chicago began charging a 7-cent fee on each paper or plastic checkout bag, and shoppers quickly began bringing their own bags. Seven cents was enough to change millions of small decisions.

Incentives also produce surprises. A school offers students a prize for every book they read. Reading goes up, but the books get shorter and thinner, because the prize rewards the number of books, not the amount of reading. That is an unintended consequence: a result the designer of the incentive did not want and did not expect. It happened because people responded to the rule exactly as written rather than to the goal behind it.

So when any rule, price or policy changes, an economist asks three questions. Who gains? Who loses? How will each of them change what they do? The answers predict behavior better than good intentions do. A policy that assumes people will ignore an incentive is usually a policy that will not work as planned.

You hold a $60 concert ticket for Saturday. Friday afternoon your manager offers you a Saturday shift at time and a half, worth $150. Notice what an economist assumes about you. You will act purposefully, comparing the pleasure of the concert against the $150 and choosing the one you value more. Economists call this being rational, which does not mean cold or greedy. It means people pursue their own goals, whatever those goals are, and respond when costs and benefits change.

Economists also build models. A model is a simplified picture of how something works, like a subway map that leaves out every street to show the lines clearly. The most useful modeling tool has a Latin name, ceteris paribus, which means other things being equal. To see the effect of one cause, hold everything else constant. If gas prices rise 10 percent, people buy less gas, other things equal. In the real world incomes, weather and car sales are all changing too, so the model isolates one thread at a time.

Finally, economists separate two kinds of statements. A positive statement describes how the world is and can be tested against evidence: raising a city’s minimum wage will change teen employment by some measurable amount. A normative statement says how the world ought to be: the minimum wage should be higher. Positive statements can be wrong; normative statements rest on values. Economists tend to agree much more about positive questions than about normative ones, and a good argument keeps the two apart.

Put the habits together and you have the economic way of thinking. Everything has a cost. People respond to incentives. Decisions happen one step at a time, at the margin, which the next chapter explains. Simple models beat no model. And when you hear an argument about the economy, ask whether it is a claim about facts or a claim about values. The rest of this course is practice in those five habits.

It is Friday night, and you have three free hours. You could babysit for a neighbor and earn $45. You could go to a movie with friends for $15. Or you could stay home and sleep. You cannot do all three in the same three hours. Whatever you pick, you give up the rest. Economists call this a trade-off: giving up some of one thing to get more of another. Each option you could choose is an alternative.

Businesses face trade-offs too. A restaurant with 2,000 square feet must decide how much space goes to tables and how much to the kitchen. More tables mean more customers at once, but a smaller kitchen that cooks more slowly. An Illinois farmer with 500 acres decides how many to plant in corn and how many in soybeans. Every acre planted in corn is an acre not planted in soybeans. The land is fixed, so more of one crop means less of the other.

Governments make the largest trade-offs. Economists often describe a nation’s budget as a choice between guns and butter: spending on defense versus spending on goods for daily life. A dollar spent on a fighter jet cannot also pay for a school lunch. Trade-offs also involve time. Suppose a pair of shoes costs $5 less at a store 40 minutes away. Driving there trades 40 minutes of your time for $5. That works out to $5 divided by two-thirds of an hour, or $7.50 an hour.

A common mistake is to think a choice has no trade-off because no money changes hands. Staying home to sleep costs nothing in cash, but it still gives up the $45 and the movie. The first step in any smart decision is to list every realistic alternative before choosing. The next lesson shows how to pick out the one alternative that matters most.

Go back to Friday night. Suppose you rank your options: first, the movie; second, babysitting for $45; third, sleeping. If you choose the movie, what did it cost? The opportunity cost of a choice is the value of the next-best alternative you give up. Here that is the babysitting. It is not the babysitting plus the sleep, because in those three hours you could only have done one of them. Listing every option you skipped is the most common mistake with this idea.

Opportunity cost counts both what you pay and what you give up. The movie ticket is $15. By going, you also give up $45 of babysitting pay. Measured in dollars, the movie costs you $15 plus $45, or $60. That is why a movie can feel cheap to a student with no job offer and expensive to one who turned down paid work for it. The price is the same for both. The opportunity cost is not.

The classic example is college. Suppose a year at a state university has tuition and fees of $12,000 and books of $1,200 (example figures). A student who goes full time also gives up a job that would have paid $30,000. Those lost wages are called forgone earnings. The yearly cost of college is $12,000 plus $1,200 plus $30,000, or $43,200. Food and rent are not added, because the student would pay for them either way.

Opportunity cost is personal because each person’s next-best alternative is different. A star athlete offered a professional contract gives up far more to attend college than a student with no such offer. None of this says college, or a movie, is a bad choice. It says the choice is worth it only when its benefits are larger than its full opportunity cost. Seeing that cost clearly is the first habit of economic thinking.

Sam spends the summer running a lawn-mowing business in Naperville. He takes in $4,000 from customers. He pays $600 for gas and repairs and $400 to rent a mower. Those payments are explicit costs: money actually paid out to someone else. Subtract them from what he took in and Sam’s accounting profit is $4,000 minus $1,000, or $3,000. On paper, the summer looks like a success.

But Sam had another offer. The city pool wanted him as a lifeguard for the summer at a total of $3,500. By mowing lawns, he gave that up. The value of that lost opportunity is an implicit cost: a cost that does not involve paying anyone, but is still real. It is the opportunity cost of using his own time in his own business. Owners often forget it because no bill ever arrives for it.

Economists count both kinds of cost. Economic profit is revenue minus explicit costs minus implicit costs. For Sam that is $4,000 minus $1,000 minus $3,500, which equals negative $500. In money terms, Sam would have been $500 better off at the pool. His business earned an accounting profit and an economic loss at the same time. Both numbers are correct; they answer different questions.

Does that mean Sam chose badly? Not necessarily. Maybe he liked being his own boss, or learned skills a lifeguard job would not teach. Those benefits are real even without a price tag. What economic profit does is put the full cost on the table, so Sam can ask whether those other benefits were worth at least $500 to him. That is a much better question than the one the accounting profit answers.

Imagine a small country that makes only two goods, food and machines. It has a fixed amount of land, workers, tools and know-how. If it puts everything into food, it makes 100,000 tons of food and no machines. If it puts everything into machines, it makes 50,000 machines and no food. Between those extremes lie many mixes. Economists list them in a table and, when they draw them, call the line the production possibilities curve, or PPC.

Here is the table for this example, with food in thousands of tons and machines in thousands. Point A: 0 machines, 100 food. Point B: 10 machines, 95 food. Point C: 20 machines, 85 food. Point D: 30 machines, 65 food. Point E: 40 machines, 35 food. Point F: 50 machines, 0 food. Every point in the table uses all of the country’s resources. Picture the points on a graph with machines across the bottom and food up the side, joined by a curve that bends outward.

A point on the curve is efficient: the country cannot make more of one good without making less of the other. A point inside the curve means resources are being wasted. Suppose the country makes 20 machines and 60 food. Point C shows it could make 20 machines and 85 food, so 25,000 tons of food are being lost. This happens when workers are unemployed or factories sit idle, as in a recession. These are unemployed resources.

A point outside the curve is unattainable with today’s resources and technology. The country cannot make 30 machines and 80 food, because at 30 machines the most food it can make is 65. The PPC turns scarcity into a picture. It shows the limit, the trade-off along that limit, and the waste inside it. It also sets up the next question: why does moving along the curve cost more and more?

Use the food and machines table to measure the cost of each step. Going from A to B, the country gains 10 machines and gives up 5 food, so each machine costs half a ton of food. From B to C, 10 more machines cost 10 food, or 1 ton each. From C to D, 10 machines cost 20 food, or 2 each. From D to E, they cost 30 food, or 3 each. From E to F, the last 10 machines cost 35 food, or 3.5 each. The more machines the country makes, the more each additional one costs.

This pattern is called the law of increasing opportunity cost. The reason is that resources are specialized: they are better at some jobs than others. When the country starts making machines, it moves the workers and land best suited to machines and least useful on farms. Little food is lost. But as it keeps going, it must pull in skilled farmers and the richest farmland. Each of those makes few machines and was producing a lot of food.

The increasing cost is what bends the curve outward, away from the origin. If resources were equally good at both jobs, the cost would stay the same at every step and the curve would be a straight line. That is called constant opportunity cost. A student splitting study time between two similar subjects might face it: each hour moved from one to the other costs about the same amount of learning in the other.

A common mistake is to read the curve’s shape as a statement about what people want. It is not. The PPC shows only what the economy can make. Which point it picks depends on the choices of its people or government. The bow shape tells you something useful for any decision: going all-in on one thing gets expensive, because the last resources you move over are the ones worst suited to it.

Suppose the country in our example discovers a better way to build machines. With the same workers and land, it can now make 60,000 machines instead of 50,000 if it makes no food, and more machines at every level of food. The whole curve moves outward. Combinations that were unattainable last year are now possible. That outward shift is economic growth: an increase in the economy’s capacity to produce.

Growth has a few main sources. More resources shift the curve out: more workers, more usable land, more factories. Better technology shifts it out, as when hybrid seed raised corn yields or computers sped up design. More human capital shifts it out, because trained workers produce more in the same hours. A shift can also go inward. A war, a flood or a pandemic that destroys factories or keeps people from working shrinks what the economy can make.

Moving from a point inside the curve to a point on it is not growth. It is putting idle resources back to work. Growth means the limit itself moves. Here is where today’s choices matter. Capital goods are machines, tools and buildings used to make other things. Consumer goods are things people use up directly, like food, clothes and phones. A country that makes more capital goods today gives up some consumption now, but it will have more tools to work with later.

Compare two countries with the same curve this year. Country X chooses 40 percent capital goods and 60 percent consumer goods. Country Y chooses 10 percent capital goods and 90 percent consumer goods. People in Y live better this year. But X is building more factories and equipment, so ten years from now its curve is likely to have moved out much farther. The choice between them is a trade-off between the present and the future, the same one a student makes by studying tonight.

A coffee shop closes at 8 p.m. The owner wonders whether to stay open later. The question is not whether the shop should exist, or whether it is profitable overall. The question is about one more hour. In economics, marginal means additional or extra. The marginal benefit is what you gain from one more unit of something. The marginal cost is what you give up for that one more unit. Comparing the two is called thinking at the margin.

Here are the owner’s numbers (example figures). Staying open from 8 to 9 would bring in $120 in extra sales. Staying open from 9 to 10 would add $70. From 10 to 11, only $40. Each extra hour costs $60 for a worker, electricity and supplies. The first extra hour adds $120 and costs $60, so it is worth it. The second adds $70 and costs $60, still worth it by $10. The third adds $40 and costs $60, a $20 loss. The owner should close at 10.

The rule is simple. Keep doing more of something as long as the marginal benefit of the next unit is greater than or equal to its marginal cost, and stop when it falls below. Notice that the owner did not look at the average sales for the whole day. A shop that averages $150 an hour over the day can still lose money in its last hour. Mixing up the average with the marginal is a common and costly mistake.

Thinking at the margin also explains a puzzle that Adam Smith noticed. Water is necessary for life and cheap. Diamonds are not necessary and cost a fortune. The answer is that prices reflect the value of one more unit. Water is so plentiful that one more gallon adds little. Diamonds are so scarce that one more is worth a lot. In the story, Devon’s next shift was worth less to him than his first because he had already worked 14 hours that week.

You paid $60 for a concert ticket that cannot be refunded or resold. On the night of the show you have a bad cold, it is pouring rain, and a friend invites you to a quiet movie night at her house. Many people drag themselves to the concert anyway, saying they cannot waste $60. But the $60 is gone whether you go or not. It is a sunk cost: money, time or effort already spent that cannot be gotten back.

The only question that matters is about the future. Which will you enjoy more tonight, the concert with a cold in the rain or the movie night? Compare only the costs and benefits that still depend on your choice. Economists call those relevant costs. The ticket price is not one of them, because nothing you do tonight changes it. In the story, Devon’s $10 basketball ticket was sunk too. His real choice was between the game and the $90 shift.

Businesses make the same mistake on a larger scale. Suppose a company has spent $2 million building a new app. Finishing it will take another $1 million, and the company now expects it to earn only $800,000 in sales. Managers who think about the $2 million already spent may push ahead to avoid wasting it. But the $2 million is sunk. Going forward, spending $1 million to earn $800,000 loses $200,000. The right move is to stop.

Letting a sunk cost drive a choice is called the sunk cost fallacy. It keeps people in bad investments, failing projects and even classes or teams they no longer want. Ignoring sunk costs is not the same as ignoring lessons. The money spent can teach you something for next time. It just cannot be recovered by spending more. Good decisions look forward, not back.

Jordan is a junior deciding whether to take a college course at a community college this summer. The class meets weekday mornings for six weeks. He could work those same hours at a grocery store. To decide, he uses cost-benefit analysis: a step-by-step way to weigh a choice. Step one, name the options. Step two, list every cost, including opportunity costs. Step three, list every benefit. Step four, put dollar values on what you can and compare.

The costs, with example figures: tuition of $450 and books of $100, which are explicit. He also gives up 10 hours of work a week for 6 weeks, or 60 hours, at $15 an hour. That is $900 of forgone earnings, an implicit cost. Total cost: $450 plus $100 plus $900, or $1,450. The main benefit: the three credits will transfer to the state university he plans to attend, where the same course would cost about $1,500 in tuition.

Compare. Benefits of about $1,500 minus costs of $1,450 give a net benefit of $50. In money terms the class barely wins. That is where the benefits without a price tag come in. Jordan gets a taste of college work, a line on his applications and a lighter load as a freshman. Against that, he loses summer free time and six weeks of work experience. These are nonmonetary costs and benefits: real, but hard to put in dollars.

Cost-benefit analysis does not make the decision for you. When the numbers are close, as here, your own values decide. When they are far apart, the numbers usually settle it. Its real power is making you count what people forget: forgone wages, time and the next-best alternative. Governments use the same method, on a bigger scale, when they decide whether a new highway or a flood wall is worth what it costs.

Ana and Ben share an apartment and have two hours on Sunday to make sandwiches for the week and fold laundry. In one hour Ana can make 6 sandwiches or fold 12 shirts. Ben can make 2 sandwiches or fold 8 shirts. Ana is faster at both jobs. When a person can produce more of something with the same time, she has an absolute advantage in it. Ana has an absolute advantage in both. Does that mean she should do everything?

Look at opportunity cost. For Ana, one sandwich costs 2 shirts, because 12 shirts divided by 6 sandwiches is 2. For Ben, one sandwich costs 4 shirts, because 8 divided by 2 is 4. Ana gives up less to make a sandwich, so she has the comparative advantage in sandwiches: the lower opportunity cost. For shirts it flips. One shirt costs Ana half a sandwich, but costs Ben only a quarter of one. Ben has the comparative advantage in folding shirts.

Now compare two plans. If each spends one hour on each job, Ana makes 6 sandwiches and 12 shirts, and Ben makes 2 sandwiches and 8 shirts. Together: 8 sandwiches and 20 shirts. If they specialize, Ben folds for both hours, making 16 shirts. Ana makes sandwiches for 90 minutes, which is 9, and folds for 30 minutes, which is 6 shirts. Together: 9 sandwiches and 22 shirts. Same people, same two hours, more of both. That extra output is the gain from specialization.

Adam Smith saw the same thing in a pin workshop. He described ten workers who split pin-making into separate steps and together made more than 48,000 pins a day, while one person doing every step alone could hardly make twenty. Splitting a job into steps done by different people is the division of labor. It is why a Chicago hospital has surgeons, nurses and billing clerks rather than doctors who do everything. Unit 8 returns to comparative advantage between whole countries.

You buy an iced coffee for $4. You would have paid up to $6 for it on a hot afternoon, so you walk away feeling $2 better off. The shop’s cost to make it, counting milk, ice, cup and the worker’s time, is $3, so it is $1 better off. Nobody was tricked. Each side gave up something it valued less for something it valued more. That is why a voluntary exchange happens at all. Together, the two sides are $3 better off than before.

This means trade is not a zero-sum game, where one side’s gain is exactly the other’s loss. A poker pot is zero-sum: whatever one player wins, the others lose. A voluntary trade is positive-sum. Value is created because the coffee moved from someone who valued it at $3 to someone who valued it at $6. The extra satisfaction both sides get is called the gains from trade.

Specialization only works because of trade. Ana makes sandwiches and Ben folds shirts, and then they share. Illinois farmers grow corn and soybeans far beyond what they could eat, then sell the crop and buy trucks, phones and medicine. Chicago became a trading center for exactly this reason. The Chicago Board of Trade, founded in 1848, gave farmers and grain buyers one place to meet and agree on prices. Specializing and trading make people dependent on each other, a condition called interdependence.

Trade does not help everyone equally, and later chapters look at who wins and who loses when it grows. A trade can also go wrong when one side is lied to or forced, which is why laws against fraud matter. But the core idea holds. When two people agree freely to a trade, both expect to be better off, or they would say no. That simple fact, repeated millions of times a day, is the engine of a market economy.

Maya is 18 and earns $25,000 a year at a warehouse (all numbers in this lesson are examples). She is thinking about a one-year welding certificate at a community college. Tuition and gear cost $7,000. She would work less during the program and lose about $15,000 in pay. So the full cost is $7,000 + $15,000 = $22,000. The pay she gives up is an opportunity cost, and it is often bigger than the tuition.

Now the benefit. Suppose certified welders near Maya start at $37,000 a year. That is $12,000 more than her warehouse job. Divide the cost by the yearly gain: $22,000 / $12,000 is about 1.8. After about two years of work, the certificate has paid for itself. Every year after that is extra income. Economists call the skills and knowledge a person builds human capital, because like a machine it costs money now and pays off later.

There are many paths. A four-year degree costs more and takes longer, but on average it leads to higher pay over a career. An apprenticeship lets a person earn a wage while learning a trade, such as electrician or plumber, so the opportunity cost is small. Bureau of Labor Statistics data show every year that workers with more education earn more on average and are unemployed less often. Averages do not decide for any one person, though.

A good decision weighs more than the average. How long will the program take? Will you borrow, and at what interest rate? Do jobs in that field exist where you want to live? Will you finish? A common mistake is to count only tuition and forget the lost pay. Another is to assume a credential guarantees a raise. The return on investment is the gain compared with the full cost, and it differs from person to person.