>I don't know a single person who had an extremely cushy childhood who is 'on fire' for anything or striving for greatness.

You could argue our current president had a pretty cushy childhood. Not sure if he's 'on fire' or 'striving for greatness' though.

Social mobility is heavily determined by a combination of race, IQ, gender, social-class, where you were born, and physical / mental health. All of that is dictated by luck when you are born. Our ego tries to convince us that we're "self made" but for the most part life is determined by "luck of the draw".