Deception and self-deception.

There is ample evidence that the average person thinks he or she is more skilful, more beautiful and kinder than others1,2 and that such overconfidence may result in substantial personal and social costs3-8. To explain the prevalence of overconfidence, social scientists usually point to its affective benefits, such as those stemming from a good self-image or reduced anxiety about an uncertain future9-13. An alternative theory, first advanced by evolutionary biologist Robert Trivers14-16, posits that people self-deceive into higher confidence to more effectively persuade or deceive others. Here we conduct two experiments (combined n = 688) to test this strategic self-deception hypothesis. After performing a cognitively challenging task, half of our subjects are informed that they can earn money if, during a short face-to-face interaction, they convince others of their superior performance. We find that the privately elicited beliefs of the group that was informed of the profitable deception opportunity exhibit significantly more overconfidence than the beliefs of the control group. To test whether higher confidence ultimately pays off, we experimentally manipulate the confidence of the subjects by means of a noisy feedback signal. We find that this exogenous shift in confidence makes subjects more persuasive in subsequent face-to-face interactions. Overconfidence emerges from these results as the product of an adaptive cognitive technology with important social benefits, rather than some deficiency or bias.