I've noticed this is more common than I expected and seems to happen when two conditions are present: (1) the person is an outsider so can ask "dumb" questions

I've noticed this is more common than I expected and seems to happen when two conditions are present: (1) the person is an outsider so can ask "dumb" questions that make you think through the foundational assumptions of your work. (2) they've experienced many failures themselves so they know what questions really matter. i.e. perhaps it's not so much that Gates is a genius (he is) as much as the above conditions are present. The corollary for me, as a startup founder, has been that I should be asking these basic questions of myself regularly (a good marketing person helps) and I've got to be careful with cash burn so I have time to learn from failures.