Here’s the core idea: a sunk cost is anything you’ve already spent — time, money, energy — that you can’t get back. The sunk cost fallacy is when you keep going with a bad decision *not* because it’s actually a good choice, but just because you’ve already put so much into it. Cleveland Clinic describes it as a cognitive bias — basically a glitch in how your brain thinks — that clouds your judgment without you even realizing it.
You’ve probably felt this. You’re halfway through a movie and it’s awful, but you think, ‘Well, I already watched an hour of it.’ Or maybe you’ve worked on a project for weeks and it’s clearly not working, but walking away feels like wasting all that effort. That feeling is real — but it’s also misleading you. According to Greater Good at UC Berkeley, a big reason we fall into this trap is our fear of loss. Quitting feels like admitting that everything we already put in was for nothing. And the more we’ve invested, the stronger that pull to keep going tends to get.
The NIH’s Office of Intramural Training and Education points out that this shows up big in career decisions too. They give real examples: pre-med students who feel locked into going to medical school just because they chose that major, or researchers who keep grinding on a topic for years past when it stopped making sense — simply because they’ve already spent so much time on it. This happens because humans aren’t purely rational. We’re emotional, and we’re wired to stick with our past choices even when new information says we should change course. That’s called commitment bias, and it’s a huge part of why the sunk cost fallacy has so much power over us.
So what do you actually do with this? The key move is shifting your question. Instead of asking ‘How much have I already put into this?’, ask ‘If I were starting fresh today, would I choose this?’ If the honest answer is no — if the job, the friendship, the class, the game, whatever it is — isn’t worth it on its own merits right now, then past investment shouldn’t be the reason you keep going. The past is gone either way. The only thing you can actually control is what you do next.
The single most important thing to remember: past costs don’t make a bad choice better. Every day you keep going is a new decision — make it based on where you’re headed, not where you’ve been.