Doing things well requires both intelligence and conscientiousness. Misplaced arrogance may lead to sloppiness which is the opposite of conscientiousness. This is a big problem in areas where there is a cost to undoing mistakes. Math is an area where there is little cost to mistakes but even here thinking before starting on an idea can save time. I think the best way to develop conscientiousness is to play a game like Go
where you are punished for making mistakes.