I have read otherwise recently, although I forget where (possibly Kahnemann - Thinking Fast and Slow, although I don't think so). I don't have sources to hand,

I have read otherwise recently, although I forget where (possibly Kahnemann - Thinking Fast and Slow, although I don't think so). I don't have sources to hand, but a quick google suggests the following: Although people subjectively rate their performances better than an objective observer would (see, e.g. http://en.wikipedia.org/wiki/Overconfidence_effect http://en.wikipedia.org/wiki/Overconfidence_effect), being overconfident can actually lead you to increase your perfomance, at least according to http://econpapers.repec.org/paper/lmumuenec/11885.htm http://econpapers.repec.org/paper/lmumuenec/11885.htm "Abstract: This paper suggests a potential rationale for the recent empirical finding that overconfident agents tend to self-select into more competitive environments (e.g. Dohmen and Falk, forthcoming). In particular, it shows that moderate overconfidence in a contest can improve the agent's performance relative to an unbiased opponent and can even lead to an advantage for the overconfident agent in absolute terms." So that isn't overwhelming evidence, but it does suggest that what you wrote might not be correct.