Or at least a sorta-wealthy family, and the further "foresight" to be in the exact right place at the right time.

That's the background of most of the Western ultra-rich, just as a consequence of there being vastly more sorta-wealthy families than already ultra-rich ones. Some of them are bound to stumble into situations that add a digit or two to their net worth. For an example, Elon Musk is notable for being tangentially involved in a huge success like three times, despite being a well-known moron.

My favourite introduction to the mathematical modeling of how inequality happens.