I took a name randomly from your list, Sheldon Adelson:

“He began his business career at the age of 12 when he borrowed $200 from his uncle (equivalent to $3,385 in 2023) and purchased a license to sell newspapers in Boston.[23] In 1948, at the age of 15, he borrowed $10,000 (equivalent to $126,814 in 2023) from his uncle to start a candy vending-machine business.[24]”

I am not disputing that it’s possible to go from rags to riches. But don’t you find it ironic that a list of people who supposedly fit the description, doesn’t actually fit the description?

Where’s my rich uncle?

https://en.m.wikipedia.org/wiki/Sheldon_Adelson

Francois Pinault is French, and inherited a family business, that’s quite an upstart.

Rowling was British and had genuine financial issues, but lucked out with her book.