By that point, he'd already been CEO of PayPal for a bit (after co-founding X.com that merged into the company that became PayPal) and made $175M for his stake

By that point, he'd already been CEO of PayPal for a bit (after co-founding X.com that merged into the company that became PayPal) and made $175M for his stake when eBay bought it. Then $100M went to found SpaceX. But that does seem like a very large bet that millionaires don't often make.