There was an interesting social science paper a few years ago.
Subjects were given a skills test. Without knowing the results, they were asked to evaluate their own performance. They were then shown someone else's test, and asked to re-evaluate.
The consistent result was that the worst performers consistently evaluated themselves as much better than average, and even upped that evaluation when shown the other paper. The complete opposite was true for the over-achievers.
US students have close to the worst performance in mathematics in the industrialized world, yet rate themselves as 'A'. The South Koreans, who are the best, rate themselves as 'C'.
My own experience with students and faculty supports this. Poor students usually assume that they are doing well. The most educated of my colleagues are hesitant outside their areas of expertise.
That feeling of inadequacy of the best and brightest drives them to excellence. I always think of M.C.Escher, and his quote that 'I wish I could draw better'. Many other famous scientists and artists expressed similar sentiments, and produced wonders.
The fact that our brains appear to be hard-wired to equate confidence with leadership means that we are much more likely to pick our managers and politicians on the basis of self-assurance, rather than ability. This is supported by other studies, showing that taller and better-looking people earn more money and are promoted more often.
This habit of choosing confident 'feel-good' individuals over hesitant problem-solvers goes a long way to explain why US voters overwhelmingly rejected President Carter in favour of Ronald Reagan.