Confidence is an essential ingredient of success in a wide range of domainsranging from job performance and mental health, to sports, business, andcombat. Some authors have suggested that not just confidence butoverconfidence-believing you are better than you are in reality-is advantageousbecause it serves to increase ambition, morale, resolve, persistence, or thecredibility of bluffing, generating a self-fulfilling prophecy in whichexaggerated confidence actually increases the probability of success. However,overconfidence also leads to faulty assessments, unrealistic expectations, andhazardous decisions, so it remains a puzzle how such a false belief couldevolve or remain stable in a population of competing strategies that includeaccurate, unbiased beliefs. Here, we present an evolutionary model showingthat, counter-intuitively, overconfidence maximizes individual fitness andpopulations will tend to become overconfident, as long as benefits fromcontested resources are sufficiently large compared to the cost of competition.In contrast, "rational" unbiased strategies are only stable under limitedconditions. The fact that overconfident populations are evolutionarily stablein a wide range of environments may help to explain why overconfidence remainsprevalent today, even if it contributes to hubris, market bubbles, financialcollapses, policy failures, disasters, and costly wars.
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