Sunk Cost

A past cost that cannot be recovered and should not drive decisions.

A sunk cost is money already spent and unrecoverable, so it should be irrelevant to future choices. The sunk cost fallacy is the tendency to keep investing in a losing endeavor because of what is already committed, rather than judging it on future prospects alone.

Refusing to abandon the failing project just because of money already spent was a classic sunk cost trap.