Have you ever kept a failing relationship tottering along because of the heartache it's already caused you? Or eaten far too much at an "all you can eat" fixed-price buffet just to get your money's worth? Were you swayed to patriotic fever pitch by arguments that the Vietnam War or the troubles in Northern Ireland must continue because anything less than a total victory would mean that lives already lost were sacrificed in vain? If the answer to any of those questions is yes, then you too have been a victim of what psychologists call the "sunk-cost fallacy"—the human tendency to judge options according to the size of previous investments rather than the size of the expected return. Truly rational choices would be made only after weighing up future costs and benefits. Past costs and benefits are quite irrelevant.
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