I googled on challenge yourself and stumbled upon Finer Minds. There you can find lots of interesting articles about self-improvement.
I read an article about falling into the self-improvement trap, which is when you learn something but don´t apply it. The things you´ve learned don´t stick for some reason. It can be that you learned things that you really don´t have any use for or interest to continue practising in real life, or that the learningprocess wasn´t that vital. I have a history of learning random things from books and the internet, things that I either didn´t learn well enough, or didn´t put in a bigger picture, or silly things like... making balloon-animals. :) They take a lot of time and effort from real knowledge which accumulated will lead to wisdom.
Lesson learned: I have to see that I use the gained knowledge from the challenge for it to be worthwhile. To find worthwhile goals I have to set up the big plan.