The sunk cost fallacy is the tendency to keep investing time or money into something simply because you have already invested in it, even when continuing no longer makes sense. The money already spent is gone regardless of what you decide next, but it still influences the decision.
This shows up financially in many ways: staying in a bad investment hoping to break even, finishing an expensive subscription you no longer use because you already paid for the year, or continuing a costly hobby because of the money already put into equipment.
The healthier question is not what you have already spent, but what makes the most sense going forward from today. Past spending cannot be recovered by continuing a decision that no longer serves you. This is educational information only.