Ever read up on it? Top performers often doubt their results are more than luck. They see the accomplishments of those better than them or with more striking contributions and judge themselves, downplay their own achievements,- which are often substantial.
Or is it humility?
Imo, the opposite of the overconfidence on Chance threads. Thse kids aren’t close. The concept has been around a long time. One author claimed he could (almost) tell someone was highly accomplished based on this modesty.