I think this is exactly what drives him.
I am ashamed to admit if I had the money he had when 24, I would have retired to some exotic places or relentlessly travelling the world.
Hes instead running two of the most disruptive firm in the world working 80 hours week.
Im not ashamed to admit that I would have retired too.
Some people need to be on the go all the time, its what keeps him relatively sane probably.
I wonder if I really could retire if (when) BTC hits $100K. It's a nice dream, and I'm sure it'd be nice for a while. But I'm pretty sure I'd go nuts unless I found some kind of project/job to take on.
Designing and building my own house could be one such project. Always quite fancied that... Grand Designs has a lot to answer for.
"Retiring" doesn't mean stopping working at all. For me it would be just a milestone in which I have secured enough assets to make sure I can live on that for the rest of my life (unless something really catastrophic happened). You will still need to take care of your money, assets, new projects, etc... It's just that you are financially free now if you don't do anything stupid afterwards.
Some people do it wrong though... And decide to start spending too much or recklessly go into risky business with the potential of being rekt.
Some people are so used to work every day on a regular job that their lifestyle is so much dependent on it that they wouldn't know how to adapt to their new lifestyle AND RESPONSIBILITIES (take care of your wealth in a safe way).
Designing and building your own home (and REALLY time consuming if you want to do it right) looks like a great project to spend some of your wealth, yeah.