he has billions but never spent more than a middle class lifestyle. Saving money matters a lot when we're talking compounding over decades.

Middle class? He owns a private jet and wears custom-designed suits. He appears to live moral frugally than most billionaires, but he hardly has a middle class lifestyle.

He famously has said he will donate most of his money rather than leave it to his children.

https://givingpledge.org/pledger?pledgerId=177

He's not leaving them zero or anything, and three of the foundations he's funding are run by his three children, so they benefit from his wealth. But they won't receive most of it.