Though used in a different context, I thought these words from G. K. Chesterton’s Orthodoxy expanded on what I was saying earlier:

Actors who can’t act believe in themselves; and debtors who won’t pay. It would be much truer to say that a man will certainly fail, because he believes in himself. Complete self-confidence is not merely a sin; complete self-confidence is a weakness. Believing utterly in one’s self is a hysterical and superstitious belief like believing in Joanna Southcote: the man who has it has ‘Hanwell‘ written on his face as plain as it is written on that omnibus.