The child spent the next few days and weeks playing with the "Nimbus 2000" and was the envy, pride, and inspiration of many. Of course, after some time, the child returned to normalcy and played games, studied, experimented with computers, wrote code, and many other fun things.
Hedonic Adaptation[1] is the tendency to return to a relatively stable level of happiness despite major events or life changes.
It might not be so binary, i.e. maybe 40% of his assets are liquid and equal to $1bn, but the point stands.
Many people who achieve things don’t want to sit still and have a lot of things they want to still do. From personal observation (reading articles and meeting people), I would say; the richer, the less inclined to stop working. Even smaller scale: where I live, people with 100ks in the bank and a house are more likely to do nothing but play golf, eat and drink and go out far more than people who have a few million. The latter, even when old (up to 80 and over) cannot sit still and usually are on boards, write books, do up and flip houses, etc.
Everyone asks this question and replaces billionaire with any other number. Some people just love to work on certain things and it makes them happy.
Some people don't work for the moeny.