only to find I completely don't understand why I wrote it the way I did in the first place.

Now that's a good time for a comment or two. At least the second time around :)

Of course, when you're in zone of the coding, you don't always recognise the things that'll throw you later.

And some would no doubt use that as a justifiction for commenting everything, every time. But yah boo sucks to that.