I’ve experienced burnout. (Probably while producing a lot of the docs you consumed learning go, btw ;)
Like I said, I agreed with my parent post’s points on just working 9-5 (on average I probably work less than that), but I just think it’s important to try to do things really, really well, but within the constraints of having a balanced life.
I spent much of the Easter weekend learning Go, and to me that was a solid investment of my time. I do not make a habit of coding extracurricularly though. If I want to hone my skills or work on a personal project, I'll do this in dead time during my fulltime work.
As an exercise, it is better to improve your ability to get things done within the 9-5 window than to allow that to balloon into your personal time.
You can still strive for excellence without running yourself fullsteam into burnoutland.