Mantaining a course of action that can no longer bring any positive outcome just because a sacrifice was made in order to make it possible.
Refusing to give up something with zero (or even negative) utility/value on the basis that a cost was paid for it.
Believing that the sole act of keeping something with zero (or even negative) utility/value can somehow retroactively make the cost paid for it worth making.
General form:
"Something was lost in order to gain A, therefore A is still better than nothing."
"If I stop doing A, then the sacrifice made for it will be for nothing."
Typical example:
"This food is disgusting."
"Then why are you eating it?"
"I still paid for it. If I threw it away, the money I spent would be for nothing."
If something has zero or negative utility, the fact it required some sort of payment/sacrifice does not retroactively give it value. Losing something for nothing at all is still preferrable than losing something for something bad.