The Trap of Past Investment

You have been watching a terrible movie for an hour. You want to leave, but you paid $15 for the ticket. So you stay. That decision just cost you two more hours of misery, and the $15 is gone either way.

The fallacy feels rational because abandoning an investment feels like wasting it. But the investment is already wasted. The only question that matters is: from this moment forward, what is the best use of your time and money? The $15 is irrelevant. It is gone whether you stay or leave.