This is purely anecdotal but, most of the people I've met perceive a ceiling to their own potential. But, I know of less than a handful who refuse to accept the existence of a ceiling and as such nothing will stop them. I'm not claiming it is a cause of determination but it is at least a factor and I argue it is a feature found in most founders in your set of successful startups (accounting for dumb luck and randomness by not saying all founders).