fallacy

Sunk cost fallacy

Also called: Concorde fallacy

The sunk cost fallacy continues a course of action because of resources already spent, rather than because of its future costs and benefits.

How it works

Money, time or effort already spent cannot be recovered whatever is decided next. Letting them drive the decision leads to throwing good money after bad.

Examples

"We've already spent three years and millions on this system, so we have to finish it."

The past spending is gone either way; the question is whether finishing is worth the remaining cost.

"I paid for the ticket, so I'll sit through the whole bad film."

The ticket is paid whether you stay or leave; staying only costs more time.

How to spot it

"We've come too far to stop."
Past investment is the main reason given to continue.
No comparison of future costs and benefits.

How to respond

Ask: if we were starting today, would we choose this?
Compare only future costs and benefits of each option.
Treat stopping as a legitimate option, not a failure.