I am big fan of "circle of competence" as Warren Buffet with Charlie Munger describe it. But I stole it to drive my learning approach. Learning is investment s

I am big fan of "circle of competence" as Warren Buffet with Charlie Munger describe it. But I stole it to drive my learning approach. Learning is investment so I would say learn mostly in your area of competence to get better. Of course you want to broaden your area with time so you might spend 80-90% of your learning time on things that are directly in your area of competence. Then 10% or 20% to broaden that, when you start using those new things they will become your circle of competence and then you can go deeper with learning about those. If you won't use those - ditch those and go find another 20%. Downside to this approach is that you need a starting point like "should I be a Python dev or Ruby dev" which mostly is asked by new fresh starters - and my answer is pick one, if it sticks and is your 80% (even if it is not really) continue if not go for another one. I had link to article by Kent Beck who advises something similar so I also copied a lot of that approach from his article. Unfortunately I don't have a link now.