persuasion
Sunk cost fallacy
What is the sunk cost fallacy?
The sunk cost fallacy is letting money, time or effort you have already spent - and cannot get back - keep you committed to something that is no longer worth it. The only sound question is what the next step is worth; the fallacy answers a different one - what you would be "wasting" by stopping.
Also known as: sunk cost effect, throwing good money after bad, escalation of commitment
The demo
A course you have stopped enjoying. Switch between counting what you have already spent and looking only at the choice ahead - and watch "finish it" quietly turn back into a real question.
"Mastering watercolours" - 10-hour course
£80 paid 6 of 10 hours watched
You have come this far. Do you finish the last four hours, or stop?
With the £80 and six hours in view, finishing feels like the way not to "waste" them.
What this demo shows (text version)
The same decision is shown two ways. In "counting what you've spent", the card highlights that you have already paid £80 and watched six of ten hours, then asks whether to finish the last four hours or stop. Framed this way, stopping feels like wasting the £80 and the six hours, so people lean towards finishing.
In "just the choice ahead", the spent money and time are removed and the question becomes only: knowing what you now know, are the next four hours worth it? The £80 and the six hours are gone either way - they cannot be recovered by continuing - so they should not weigh on the decision at all. That is the sunk cost fallacy: letting unrecoverable past spending drive a choice that is really only about what comes next.
The £80 and six hours were gone the moment you spent them, whichever button you press. The only real choice left is whether the next four hours are worth it - and the instant the demo stops reminding you what you have sunk, that answer gets a great deal clearer.
Sunk cost is loss aversion wearing a calendar: stopping feels like wasting what you put in, so you pour good time after bad to avoid admitting the loss. But the loss already happened. Separating what is genuinely recoverable - usually only the effort still ahead - from what is already spent is the whole escape route.
Products lean on this hard. "You are 80% set up", progress bars on a form you abandoned, "you have earned 4,000 points" - each is a reminder of investment, placed to make leaving feel like a loss. Notice when an interface is totting up what you have already sunk rather than what you stand to gain next.