Sunk cost fallacy
The tendency to keep going with something because of the time, money or effort already spent, even when continuing costs more than it returns. Past costs cannot be recovered, so they shouldn't drive future choices.
In everyday life
You sit through a boring, expensive concert to the very end because the tickets cost so much.
You're halfway through a 600-page novel you've disliked since chapter two, and you force yourself to finish because you've already spent so many evenings on it.
Why your mind does this
Finishing what we start is usually a good strategy, since a brain that quit at every bump would never complete anything. Valuing what we already have, what we built and what we worked for keeps us committed and protects our resources. Losing what we have can hurt more than an equal gain helps, so caution around losses often makes sense.
How to spot it
Ask whether you would start this today, knowing what you know now.
How to counter it
Decide based only on future costs and benefits, and treat what's already spent as gone either way.
Same family: Finishing what we started
SourcesArkes & Blumer (1985)·Wikipedia