Choices and persuasion
Sunk cost effect
Also called Sunk cost fallacy
People keep putting time or money into something because of what they've already spent, even when stopping would be better.
What's spent is gone whatever you decide next, but it still feels like a reason to continue. People sit through bad films they've paid for and keep funding failing projects.
Teams fall for it too: a feature that has taken months gets shipped because of the months, not because it works. Ask 'knowing what we know now, would we start this today?'
In practice
A product team that has spent two quarters on a feature user testing shows nobody wants, and ships it anyway because of the effort already made.
Common mistake
Using it against customers, such as reminding people how much they've paid to keep them on a plan that no longer suits them.
Where it comes from
Studied by Hal Arkes and Catherine Blumer in 1985, including an experiment in which theatre-goers who paid full price for season tickets attended more shows than those given discounts.