It's been difficult for me to decide what to write down and what not to. On the one hand, I may encounter an issue again, but then again, maybe I'll just remember how it works naturally if I encounter the issue frequently, so it might not be worth the time.
As an example, if I am learning git, the subtleties of the `git checkout` command would likely trip me up, but should I write that down? It is such a common command that, if I am using git regularly, I will probably remember it without having to write it down.
As another example, what if I have an issue with something that I likely won't ever use again? Say, for example, I have to get my W-2 from a former employer, and their Web site requires you to call a number that's really hard to find to reset your password and then navigate a complicated phone tree. Should I write down the mistakes I made in figuring out how to do all that? I would say probably not, because I won't have to deal with this issue again.
Finally, there is the fact that technologies change. Some things, like Unix commands, are pretty stable, whereas other things, like best practices for JavaScript, are not. How much time should I dedicate to writing things down when they are likely to change?
All of this is to say: I agree it's a good thing to document mistakes, and I should probably do that more systematically, but I think there is some art to deciding what to write down and what not to.