Comment by WJW

I think it technically only implies that at the time when he first became rich, he didn't understand why. It's possible that he has since discovered what exactly happened.

As a sibling comment already implied, the core message of the book is that the price of getting rich is often not worth it. I personally also enjoy the "Rich but not famous" essay by Tim Ferriss at https://tim.blog/2020/02/02/reasons-to-not-become-famous/ which has a lot of vivid descriptions of the downsides of fame.