Glossarytaught in M6.04, M9.03
Sunk cost fallacy
Also called sunk cost, escalation of commitment.
Continuing with a course of action because of what has already been spent, when the spending cannot be recovered and should not affect the decision.
It appears in portfolios as averaging down on a position because of the loss already taken, and in companies as continuing to fund a project because of the capital already committed.
The right question ignores history entirely. Given everything you know now, is this the best use of the next rupee?
What is spent is gone. It isn't an argument.