The Next Best Economist

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Economics in 30 Minutes — Part 1 Companion Page: Scarcity, Choices, and Models

Companion to "Economics in 30 Minutes," Part 1: Scarcity, Choices, and Models.

This page has the definitions, the sources for the quotations in the video, the questions asked in the video with room to go further, and prompts you can give an AI tutor. Work through the exercises before you read the hints at the bottom.

1. Key terms

Economics. The study of how people make choices when they can't have everything they want, and how those choices add up. The first half is about individual decisions; the second half is about what happens when many people's decisions interact in markets.

Scarcity. There is not enough of something for everyone to have as much as they want at a price of zero. Scarcity is about wants exceeding what is available, not about poverty. Time is scarce for everyone; so are beachfront land and front-row seats. A thing can be scarce in a rich country and plentiful in a poor one, or the reverse.

Opportunity cost. The value of the best alternative you give up when you choose something. It is not the sum of every alternative, only the best one; the alternatives are usually mutually exclusive, so adding them up double-counts. It can be money, time, or anything else you value. Part 4 treats it in full.

Allocation. Deciding who gets something when not everyone can have it. Prices are one way to allocate. Lines, lotteries, reservation lists, memberships, status, and political decisions are others. When the money price of something falls to zero, one of these other methods takes over; the allocation problem does not go away.

Microeconomics. The study of choices by people and firms, and of how markets interact: the market for beer, for apartments, for nurses, and how a change in one reaches the others.

Macroeconomics. The study of economy-wide outcomes: inflation, unemployment, growth, interest rates.

Model. A deliberate simplification that keeps what matters for a question and leaves out the rest. A model does not have to be realistic to be useful. The happy face in the video is a model of a feeling; a subway map is a model of a transit system; supply and demand is a model of a market. A model's usefulness depends on the question: change the question and something it left out can suddenly matter.

Ceteris paribus. Latin for "other things equal." The practice of changing one thing at a time while holding everything else fixed, so that you can see what that one thing does. In the video, erasing the mouth and drawing a frown changes one thing and changes the meaning. Economists say "all else equal" to mean the same thing. On a chalkboard it is easy; in real data, several things change together, and holding the rest fixed is much harder.

2. The quotations in the video

John Maynard Keynes, "Economic Possibilities for our Grandchildren" (1930). The essay predicts that "the economic problem may be solved, or be at least within sight of solution, within a hundred years," assuming no major wars and no large population increase. A hundred years from 1930 is about 2030. Keynes also expected people would then struggle with how to use their leisure. The essay is short and widely reprinted; a copy is in Keynes's Essays in Persuasion, and the text is online at the Economics Network's archive.

Elon Musk, VivaTech conference, Paris, May 2024 (by video link). As reported by Fortune (May 24, 2024): "In a benign scenario probably none of us will have a job. But in that benign scenario there will be universal high income—not universal base income—[and] there will be no shortage of goods or services." Also: "any job that somebody does will be optional." Source: https://fortune.com/2024/05/24/elon-musk-future-work-jobs-hobbies-artificial-intelligence/

Note the qualifier. Musk described this as the "benign scenario," not a certainty. The video's summary leaves the qualifier out for speed; this is the full wording.

Elon Musk, post on X, December 17, 2025, replying to Ray Dalio about a pledge by Michael and Susan Dell to children's savings accounts: "It is certainly a nice gesture of the Dells, but there will be no poverty in the future and so no need to save money. There will be universal high income." Source: https://x.com/elonmusk/status/2001361571407368589 (reported by Fortune, Dec. 18, 2025: https://fortune.com/2025/12/18/elon-musk-no-poverty-dalio-philanthropy-saving-accounts-trump)

The video describes these forecasts and asks the economist's question about them. It does not take a position on whether they will come true, and it is not advice about whether you should save.

3. Questions from the video, with room to go further

3.1 After scarcity and opportunity cost

1. What is scarce for you this week? Give one example that isn't money.

2. What is the best alternative you give up when you spend an hour on this lesson? Is it really the best one, or the first one you thought of?

3.2 The faces

3. Draw three faces as simple as the one in the video: surprise, anger, a wink. Change one feature at a time. Which feature carries the message in each?

4. Show your faces to someone else without telling them what they are. Did they read them the same way you intended?

5. Could exactly the same smile mean something different in another situation: sincere, polite, sarcastic? What would you need to know to tell?

6. For what question would the missing nose or ears suddenly matter?

3.3 The 90-percent-cheaper world

Set-up. Suppose new technology makes comparable housing (rent, or the cost of comparable housing services), food, and ordinary consumer goods cost 90 percent less. For now, hold your money income fixed. This is a hypothetical about abundance, not a forecast.

7. How would your life change? Which things would you buy more of? For each one, would you spend more dollars on it, or fewer? (Buying more of something can mean spending less on it.)

8. What would you do with the money left over? Spend it on something else, save it, pay off a debt, or eventually work less? You don't have to spend all of it. Explain your priorities.

9. Now let everyone adjust, and drop the fixed-income assumption. What happens in the markets people spend more on? Which businesses expand? Which jobs, wages, or incomes might change?

10. What is still scarce? Name a particular thing, not "resources."

11. How do you think it would be allocated? Who gets it, and who misses out? (This is a prediction.)

12. How should it be allocated? (This is a recommendation.) State the principle you're using: willingness to pay, need, equal chance, contribution, or something else. What tradeoff does your choice create?

Keep your answers. Part 4 returns to questions 10–12 after you have supply and demand.

3.4 A model you already use

13. Pick a model you use without thinking of it as one: a map, a recipe, a weather forecast, a résumé, a game's rulebook. Write down (a) the question it answers, (b) three things it leaves out, and (c) one situation where leaving those things out would get you into trouble.

4. Using an AI tutor

These prompts ask the AI to guide your thinking, not give answers. Paste the set-up prompt first, then the prompt for the exercise you are working on.

Set-up prompt (paste first)

> I am a student working on exercises about scarcity, opportunity cost, and what an economic model is. Act as a tutor, not an answer key. Do not give me final answers or lists. Ask me one question at a time. Make me state my reasoning before you comment on it. If I ask for the answer, remind me to try first and give me a hint instead. At the end, ask me to summarize what I concluded and what I am still unsure about.

Scarcity and opportunity cost (questions 1–2)

> Here is something that is scarce for me this week and the best alternative I'm giving up for this lesson: [paste]. Ask me whether my "best alternative" is really the best one or just the first I thought of, and whether I'm adding up alternatives I couldn't actually have done at the same time.

The faces (questions 3–6)

> I drew three simple faces: surprise, anger, a wink. Here is what I changed for each: [paste]. Ask me which single feature carried each message, whether someone else would read it the same way, and what question would make a missing feature matter. Don't explain "ceteris paribus" to me; make me explain it to you.

The 90-percent-cheaper world (questions 7–12)

> I'm working through a hypothetical where housing, food, and ordinary goods cost 90 percent less and my income stays the same. Here are my answers about what I'd buy more of and what I'd do with the leftover money: [paste]. For each item, ask me whether I'd spend more dollars or fewer, and don't let me treat "buy more" and "spend more" as the same thing.

> Now I'm letting everyone adjust at once. Here is my prediction of what changes: [paste]. Ask me which of my predictions depend on incomes staying fixed, and what happens to them when incomes can change too.

> Here is what I think would still be scarce, how it would be allocated, and how it should be: [paste]. Ask me to separate my prediction from my recommendation, and to state the principle behind the recommendation. Then ask who loses under it.

A model you already use (question 13)

> I picked [a map / a recipe / other] as a model. Ask me what question it is built to answer, then ask me to find things it leaves out. Don't suggest any. When I have a list, ask me which omission would matter most if the question changed.

Revising your reasoning

> Here is my full answer: [paste]. Play the role of a skeptical reviewer. Identify my weakest claim and ask me questions until I either defend it or revise it. Do not rewrite my answer for me.

Rules for using AI on these exercises

5. Hints (try the exercises first)

Questions 1–2. The opportunity cost of an hour is whatever you would actually have done with it instead, not everything you could have done. If your list says "sleep, exercise, and studying," pick the one you would have chosen.

Questions 3–6. Eyebrow angle, widened eyes, a round mouth, and one closed eye each carry a message with very few marks. Other people may read them differently, and the same smile reads differently at a funeral and a party. The face tells you what someone is showing, not with certainty what they feel. The missing nose matters the moment the question becomes "where do the glasses go?" A model's usefulness depends on its question.

Questions 7–9. Quantities, dollars spent, and the share of your budget are three different things; buying twice as much food at a tenth of the price means spending a fifth as many dollars on it. Saving, paying down debt, and working less are all legitimate uses of what's left. Holding your income fixed made your own choices tractable; it is not a claim that everyone's income stays fixed once everyone adjusts. When many people want more of something with limited capacity, its price, its waiting time, or some other hurdle rises. The source of the price fall and how supply responds both matter, so this is not automatically a prediction of inflation or of universal leisure.

Questions 10–12. Ask of each candidate: can a factory make more of it? Land in a particular place, a time slot, a specific original object, and a person's attention all fail that test. Energy and raw materials pass it only up to a limit. No allocation method is automatically the right answer to "how should it be allocated"; each one serves a different principle and each one has losers.

Question 13. A map leaves out building heights, traffic and weather. That is fine for finding an address and bad for planning a bike ride up a hill. The question decides what counts as a safe omission.