I guess the key here is that you can totally immerse yourself in something that doesn't feel like work; a project that fullfills you from the deepest of your heart.
That tends to happen once every 10 years.
It doesn't tend to happen in day-to-day grunt work at an AdTech shop, pushing JIRA tickets.
Every ten years or so I get stupid, I guess.
I guess I finally wised-up when I turned 51, we'll see if I stay that smart in a couple of years :-)