I once fixed a bug like that, then went wait a minute. Sure enough source control revealed I'd made exactly the same fix 2 years ago, and 2 years before that someone else had done exactly the same. In the odd years someone else undid that fix to fix a different bug that seemed unrelated. Once I figured out what the other problem was I was able to find the more complex fix for both situations.

I wished I had heard of automated tests then