Debugging with Hypotheses

I think that's the most important point of the article. If you don't understand the code you're fixing well enough to be able to explain what the bug does or why your fix fixed it, you'll have no way of knowing that (1) the bug (and not just a particular limited case of it) is actually fixed and (2) that you haven't introduced additional bugs by fixing the first one.

If you're reviewing someone's code and they can't explain to you how their fix removed the bug (e.g., they just changed random stuff around and the bug "went away"), that's a bad sign.

This happened to me so often and in such striking ways that when presented with a problem now, unless the answer is obvious, I always say I'll be sleeping on it and, no, I won't be solving it today - it's interesting how many people think this is laziness at first, and will even tell you so, but are then thankful the next day when you come up with a creative solution.