I mean what would you still doing even if you were not payed by it!
Learning more about what I always thought would be impossible to understand.
Having an overwhelmingly self-deprecating attitude and sitting alone in my apartment for decades - I've learned the skill of muscling though the confusion and frustration involved in trying to grasp well-established logic, structure and design.
Sometimes it gets the best of me, and I move onto something that I feel is more productive and rewarding - but, at least my opinion has been validated through hands-on experience (as well as similar experiences in the past, that I'd discover were trendy crap shoots encouraged by worthless agencies.)
However...
During that educational process, I'll occasionally find a game-changer - whether that title is set by me or the industry we work within - and I continue to chase the proverbial 'golden egg' with the goal of eventually teaching others about my experiences and skills learned.
I love seeing my thoughts form together as a puzzle piece. Like Mark said, finishing our projects in our spare time is hard but fun, especially when we have families and lives outside of our screens (hopefully). Another thing that really does it for me is to just feel powerful while publishing something has the ability to make others happy.
Mark
The main thing I don't do with projects in my spare time is finishing them.