Six experiments investigated people’s optimism in competitions. The studies involved hypothetical and

real competitions (course grades in Experiments 1 and 2, a trivia game in Experiments 3–5, and a poker

game in Experiment 6) in which the presence of shared adversities and benefits (factors that would

generally hinder or help the absolute performance of all competitors) was manipulated. Shared adversities

tended to reduce people’s subjective likelihoods of winning, whereas shared benefits tended to increase

them. The findings suggest that when people judge their likelihood of winning, their assessments of their

own strengths and weaknesses have greater impact than their assessments of their competitors’ strengths

and weaknesses. We identify egocentrism and focalism as two causes of the bias. The experiments

revealed moderators of this bias, but also illustrated its robust nature across a variety of conditions.