Relearning something I already knew because I forgot I already knew it. Which you figure out just as the final lesson or exercise is drawing to a close :\ It

Relearning something I already knew because I forgot I already knew it. Which you figure out just as the final lesson or exercise is drawing to a close :\ It doesn't bother me since I don't always hesitate to re-invent the wheel either, and when I do go forward I always come up with something in addition to the same old thing I was working on. When life gives you lemons, make cheesecake.