"But I'd be surprised if a significant number invested their entire net worth and time into a single endeavor." AFAIK Musk was a relative nobody in the million

"But I'd be surprised if a significant number invested their entire net worth and time into a single endeavor." AFAIK Musk was a relative nobody in the millionaire world when he poured a majority of his wealth into SpaceX (2002). They were very close to bankruptcy during the Falcon 1 experiments and if the fourth launch failed, they would have joined a fairly extensive graveyard of defunct space startups, together with Carmack's Armadillo Aerospace and a few hundred others.