Sunk Cost Fallacy: Why We Throw Good Money After Bad

You have been watching a film for forty-five minutes and you are not enjoying it. You paid for the ticket. Do you leave, or do you sit through the remaining ninety minutes in the hope that it improves?

Most people stay. And most people, if you ask them why, will say something like: because I already paid for it. From an economic perspective, this is irrational. The money is gone either way. The ticket price should have no bearing on whether the next ninety minutes of your life are well spent. But it does.

This is the sunk cost fallacy: the tendency to continue investing time, money, or effort into something because of what you have already put in, rather than on the basis of expected future returns. Sunk costs — costs that have already been incurred and cannot be recovered — should be irrelevant to forward-looking decisions. They are irrelevant in theory. In practice, they are extremely powerful.

Loss aversion, first described by Kahneman and Tversky, is part of the explanation. Losses loom roughly twice as large as equivalent gains in human psychology. When you consider abandoning a project you have invested heavily in, that investment feels like a loss. Continuing feels like keeping the loss from being confirmed. So you continue.

The effect shows up everywhere. Companies continue funding failing projects to avoid admitting the initial investment was a mistake. Countries continue fighting losing wars partly because so many lives have already been sacrificed. People stay in unfulfilling relationships or careers because of the years already spent. The escalating commitment to a failing course of action has driven some of the largest institutional disasters in business and governance.

The corrective is to regularly evaluate your ongoing commitments as if you were deciding fresh — without the history. Imagine you had not already invested. Given only what you know today and the expected returns going forward, would you choose to begin this now? If the answer is no, the sunk costs are driving your decision, not rational future-oriented thinking.

This is genuinely hard to do, not because people are stupid, but because loss aversion and consistency drive are deeply embedded. The first step is noticing when sunk cost reasoning is happening. The second step, taken honestly, is much harder: letting go of what you cannot get back.