It's a fact: 80% of people tend to think they are above average. Until now, few people have ever questioned why? What happens is that we evaluate others based on their average performance and ourselves based on our best performance.
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We examine whether people call to mind different manifestations of various traits when considering what they are like than when considering what others are like. Specifically, do people think that peak manifestations of their traits and abilities best capture who they are themselves, but that other people are better captured by their average performances or trait expressions? In Studies 1a and 1b, participants were more likely to believe that their own most attractive photographs best represent their typical appearance than others’ do. In Study 2, participants’ estimates of where they stand on various trait dimensions coincided with their highest possible standing, whereas their estimates of an acquaintance's standing coincided with the midpoint between the latter's highest and lowest possible standing. In Study 3, regression analyses revealed that students’ predictions of their own final exam score were based most heavily on their highest score received to that point, but their predictions of someone else's final exam score was based most heavily on that student's average score. We discuss how this tendency fits in the broader literature on self-other differences in evaluation and how it contributes to above-average effect.
Source: The better-than-my-average effect: The relative impact of peak and average performances in assessments of the self and others