I have a notesfile on how to fix/debug things. When I started it, I would write things down after I fixed something and figured I'd need to remember it later.

Problem was, I would often forget to write things down, or naively think "that was quick to find out, don't need to write it down", which is a classic mistake of confusing post-facto mindset with pre-facto.

So now when I wonder how to do a thing, I first write down in my notesfile what my question is, so when I do resolve it I go and write down the answer to satisfy my need for closure.