Kahneman and Tversky
Why Losing Twenty Feels Worse Than Winning Twenty Feels Good
Two psychologists set out to understand why people make terrible financial decisions, and accidentally dismantled the foundation of modern economics.
The Idea
For most of the twentieth century, economics rested on a seductive assumption: people are rational. When choosing between options, they weigh outcomes, calculate probabilities, and act in their best interest. Clean, elegant, and almost entirely wrong. Daniel Kahneman and Amos Tversky, working together at Hebrew University in the 1970s, ran a series of deceptively simple experiments that exposed the cracks. Their most enduring discovery — Prospect Theory — showed that humans don't evaluate outcomes in absolute terms. We evaluate them relative to a reference point, usually whatever we already have. And crucially, the pain of losing something is roughly twice as powerful as the pleasure of gaining the equivalent thing. This is loss aversion, and it warps nearly every financial decision you make. It's why investors hold onto failing stocks far too long — selling would make the loss feel real. It's why people decline a perfectly reasonable bet (a fifty-fifty chance of winning a hundred or losing eighty) because the potential loss looms larger than the potential gain. It's why the framing of a choice — 'ten percent chance of failure' versus 'ninety percent chance of success' — changes what people choose, even when the options are mathematically identical. What Kahneman and Tversky proved wasn't that humans are stupid. It's that we're running cognitive software that evolved for a very different environment — one where losing your food supply was catastrophic and gains were marginal. Our financial intuitions are ancient machinery operating in a modern world.
In the World
In 1979, Kahneman and Tversky published their landmark paper, 'Prospect Theory: An Analysis of Decision Under Risk,' in the journal Econometrica. It would eventually become one of the most cited papers in all of economics — remarkable, given that neither author was an economist. One of their most striking experiments involved a simple choice. Ask people: would you rather have a guaranteed sum, or a gamble with the same expected value? Most people choose the guarantee — that's just risk aversion, nothing new. But then flip the framing: instead of choosing between gains, frame both options as losses. Suddenly, people become risk-seeking. They'll gamble to avoid a certain loss, even when the expected outcome is worse. This asymmetry had real consequences. When the Chicago Bulls were negotiating contracts in the 1990s, players' agents intuitively understood that framing offers as 'avoiding a pay cut' rather than 'receiving a raise' generated more resistance to compromise. The number on the page might be identical; the psychology is entirely different. Kahneman eventually received the Nobel Prize in Economics in 2002 — Tversky had died in 1996, and the prize is not awarded posthumously. In his acceptance speech, Kahneman was careful to note that the work was inseparable from Tversky, a partnership so intertwined that their colleagues sometimes joked they shared a single mind. Their findings didn't just produce a better theory of how people behave. They created an entirely new field — behavioural economics — that now shapes government policy, retirement savings systems, and the design of every financial product you've ever been nudged into buying.
Why It Matters
Loss aversion isn't a flaw to be ashamed of — it's a feature of human cognition that served us well for millennia. But knowing it exists changes how you can engage with your own decisions. The next time you're reluctant to sell an investment that's been falling, ask yourself: would I buy this today, at this price, with fresh eyes? If the answer is no, you're probably being held hostage by loss aversion — the desire to avoid crystallising a loss, even when holding on makes things worse. The same mechanism explains why financial decisions feel harder when framed as losses. Switching pension providers, renegotiating a mortgage, cutting a subscription — these all feel like they involve giving something up, even when the numbers clearly favour moving. The discomfort is real, but it's psychological, not financial. Kahneman and Tversky gave us a gift: a mirror. Understanding that your brain weights losses twice as heavily as equivalent gains doesn't make the feeling go away, but it lets you name what's happening. And naming it is usually the first step toward not letting it run the show.
A Question to Ponder
Is there a financial decision you've been avoiding — a change, a sale, a switch — where the real reason you haven't acted is that making the move would force you to admit a loss?
Get a new one of these every morning.
Start learning with Thinkable