One of my former professors...

...writes eloquently about overconfidence.

Two lessons emerge from these papers. First, we shouldn’t expect that the competition to become a top manager will weed out overconfidence. In fact, the competition may tend to select overconfident people. One route to the corner office is to combine overconfidence with luck, which can be hard to distinguish from skill. C.E.O.’s who make it to the top this way will often stumble when their luck runs out.

The second lesson comes from Mark Twain: “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”