When you feel the need to write a comment, first try to refactor the code so that any comment becomes superfluous. - Martin Fowler

One of the things I've been trying to do is look for simpler or rules underpinning good or bad design. I think one of the most valuable rules is to avoid duplication. "Once and only once" is the Extreme Programming phrase.

People also underestimate the time they spend debugging. They underestimate how much time they can spend chasing a long bug. With testing, I know straight away when I added a bug. That lets me fix the bug immediately before it can crawl off and hide. There are few things more frustrating or time-wasting than debugging. Wouldn't it be a hell of a lot quicker if we just didn't create the bugs in the first place?

The definition I use for a pattern is an idea that has been useful in one practical context and will probably be useful in others