I re-read articles I read and didn't understand and if now I do, I learned something that allow me to better understand a wider range of subjects. If not, I did

I re-read articles I read and didn't understand and if now I do, I learned something that allow me to better understand a wider range of subjects. If not, I didn't progress. I retry puzzles that I failed to complete in the past and if they appear easier to do, I progressed. It worked for some Euler Puzzle that I couldn't begin to understand and a few months afterward they seemed trivial. Redoing anything you struggled to achieve (or didn't achieve) could be a proof of progress, as long as it's actually understood.