In XP they say "Do the simplest thing that could possibly work." I think the word 'simple' has been abused and often turns into "roll my own, quick and dirty." I'll use a common example from recent history: date manipulation.
Why wouldn't you want to use DateTime? It gives you so much for free, I consider that the quintessential simple. Instead, so many people write their own date formatter, or calculator, or whatever. Please, if you're going to use this XP theory, stop writing code!
I'll admit, I've only recently been studying XP, but it would seem I've been doing quite a lot of it for a long while. I just think that the phrase should be "Find the most useful thing that could possibly work."