In economics and business decision-making, a sunk cost is a retrospective (past) cost that has already been incurred and cannot be recovered. Sunk costs are sometimes contrasted with prospective costs, which are future costs that may be incurred or changed if an action is taken.
In traditional microeconomic theory, only prospective (future) costs are relevant to an investment decision. Traditional economics proposes that economic actors should not let sunk costs influence their decisions. Doing so would not be rationally assessing a decision exclusively on its own merits.
On the other hand, evidence from behavioral economics suggests this theory fails to predict real-world behavior. Sunk costs do, in fact, influence actors’ decisions because humans are prone to loss aversion and framing effects. In light of such cognitive quirks, it is unsurprising that people frequently fail to behave in ways that economists deem rational.
Sunk costs should not affect the…
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