Several times in my career I have found myself learning and reading and suddenly finding that what I want to do next has no blog posts, or third party frameworks - I have reached the state of the art in one (tiny) direction.

That is where the productive hobbies take you - to the point where to play some more you need to invent. At this point skills, available time all come to bear - but I now recognise this time - and refuse to waste the opportunities.

Not easy to spot for oneself - spotting it as investment - no idea :-)