Why past investment distorts future decisions
The sunk cost fallacy is the tendency to continue investing in a project, relationship, or course of action because of resources already spent, even when continued investment will not improve the outcome. A business continues a failing product line because they have already invested millions. A person stays in an unrewarding job because they have years invested. A investor holds a crashing stock because they have already lost so much. In each case, the past investment is irrelevant to whether the next step is wise.
The fallacy arises because the brain treats past expenditure as meaningful to future utility. Psychologically, walking away from a failed investment feels like accepting that the investment was wasted. Continuing feels like there is still a chance to recover. But throwing good money after bad is still throwing good money. The investment is gone regardless; the only question is whether the next dollar improves outcomes.
Reframing sunk costs out of decisions
The remedy is to reframe future decisions as forward-looking only. Before continuing investment, ask: if I had this project blank today with nothing invested, would I choose to start it? If the answer is no, continuing is a mistake regardless of past expenditure. If the answer is yes, past investment is irrelevant; continue. This simple framing eliminates the fallacy because it forces you to think only about future returns versus future costs, the only factors that matter.
The hardest cases are high-sunk-cost situations where the emotional weight of past investment is highest. A career change means admitting the previous years did not build toward the goal. Ending a relationship means the time invested was not toward a lasting partnership. Shutting down a project means years were wasted. The reframe requires accepting that sometimes time is spent and nothing accrues from that time. That pain is real, but it is not a reason to spend more.