You learn just enough to get your problems solved appropriately. What's approriate is the thing you have to judge specifically within your problem space.

If you're working on life-sustaining / life-saving problem space, appropriate better be very robust. If you're hacking on a hobby project, appropriate is whatever you feel like.

Personally I learn something new (almost) every day. Some of it is related to my work, some of it I learn just because I find it interesting. That's how I've grown to be a generalist. I didn't strive to be one, it just happened due to life long learning.