faultlinesweekly

"Don't put all your eggs in one basket" predates modern finance by centuries, but it took until the 1950s for anyone to prove mathematically why it works — and the proof turned out to be more interesting than the folk wisdom alone suggests. Diversification doesn't just spread out your bad luck. Under the right conditions, it can genuinely reduce your risk without costing you any of your expected return, which is a much stronger and stranger claim than "don't be reckless." Risk isn't just about how much an asset moves The intuitive way to think about risk is to look at how much a single investment's price bounces around — a volatile stock feels risky, a stable bond feels safe. That intuition isn't wrong, but it's incomplete, because it only looks at assets one at a time. The more complete picture asks a different question: when this asset falls, what tends to happen to the other assets in the portfolio at the same time? This second ques...

The line is often attributed to Einstein, though there's no solid record he actually said it. The attribution doesn't really matter — what matters is why the idea has stuck around for so long that people wanted a genius to have said it. Compound interest is one of the few concepts in finance that sounds almost too simple to matter, right up until you actually run the numbers over a long enough stretch of time and watch the result stop looking simple at all. The one-word difference that changes everything Simple interest and compound interest start from the same place: you earn a return on money you've invested or lent. The difference is what happens to that return. With simple interest, you earn a return only on your original amount, every period, forever. With compound interest, the return you earned gets added to your balance, and the next period's return is calculated on that new, larger total. You're no longer just earning a return on your original money — you...

Among the handful of indicators economists watch closely, few have earned the reputation of the inverted yield curve. It has preceded nearly every US recession over the past several decades, which is an unusually consistent track record for something as simple as comparing two interest rates. Understanding why it works requires understanding what the yield curve actually represents — not as an abstract chart, but as a real-time vote on the future being cast by people with money on the line. What the yield curve actually measures A government bond is a loan to the government, and the interest rate — or yield — it pays depends partly on how long you're lending the money for. Under normal conditions, lending money for 10 years carries a higher interest rate than lending it for 2 years, for a simple reason: locking up money for longer exposes the lender to more uncertainty, so lenders demand extra compensation for that risk. Plot the yields of bonds with different maturities on a cha...

Everyone experiences inflation the same way: things cost more than they used to. But that observation, while accurate, describes the symptom rather than the cause. Prices don't rise on their own — they rise because something specific changed in the relationship between how much money is chasing how many goods, and that relationship can shift for more than one distinct reason, each with a different explanation and a different remedy. Money and goods are two sides of the same equation At its simplest, an economy is a constant negotiation between how much money exists and how much stuff that money can buy. If the amount of money in circulation grows faster than the amount of goods and services available to buy, each individual unit of money ends up representing a smaller share of the total stuff — so it takes more of it to buy the same item. This isn't a policy failure or a conspiracy; it's closer to basic arithmetic. If a country doubles its money supply overnight without d...

Every few years, headlines start asking the same question: are we headed for a recession? The word gets used constantly, but the mechanism behind it — why a growing economy suddenly stops growing and starts shrinking — is usually skipped over in favor of naming whatever event happened to trigger the most recent one. Trigger events change every cycle. The underlying mechanism doesn't, and understanding it explains something the trigger-focused explanations miss: why recessions are a recurring feature of modern economies rather than a series of unrelated accidents. An economy is a chain of spending decisions The simplest way to think about an economy is as a long chain: one person's spending is another person's income. A factory worker's paycheck becomes spending at a grocery store, which becomes income for the grocery store's employees and suppliers, which becomes their spending, and so on. As long as this chain keeps moving at a healthy pace, the economy grows — m...

Ask most people why the stock market rises over time and you'll get an answer like "the economy grows" or "companies make more money." Both are true, but neither actually explains the mechanism — and the gap between "true" and "the mechanism" matters if you want to understand why this pattern has held across a century of wars, recessions, and crashes that each felt, at the time, like they might be the exception. Growth is a compounding process, not a straight line The core reason the market trends upward isn't that stocks are magic — it's that the companies inside a major stock index are, collectively, in the business of turning a smaller amount of money into a larger amount of money, year after year, and then reinvesting the result to do it again. A company that grows profits 7% a year isn't just adding a fixed amount each year; it's adding 7% of an increasingly larger base. Run that process for 20 or 30 years and the numbe...