The number of times I've spent hours trying to figure out some obscure issue only to stumble upon a multiple-years-old stackoverflow post of myself asking the same question isn't that high, but definitely higher than I'd like to admit.

I started keeping an informal "changelog" for my PC, because I was burnt out on reinstalling my OS every few months. I can be a bit patchy at actually updating it, but when I do, it's so refreshing to ask "why the hell did I install $software ?" and then to check my logs and find that I installed it while trying to solve $problem, but that it didn't work and I ended up solving the problem a different way, but forgot to remove $software. It's so nice to not be scared of breaking stuff when I've forgotten why I did things a certain way.