[nwhitehead]

This is a good one. It is all too easy to spend years casually "interested" in a topic without developing a true foundation of the important ideas in the field.

In my case I spent two decades casually reading about economics. But then one day I ordered an economics textbook to work through the problems, and found out that I basically knew nothing and couldn't do any of the problems. A few months of slowly working through the textbook gave me a much deeper level of understanding. I could do the problems now.