Ron Jeffries, when someone asks for data to “prove” that XP or some development practice works, is wont to say that the person they’re trying to convince may be asking for evidence, but it’s not likely that the evidence will convince them.

Bob Sutton recently wrote about the book Made to Stick: Why Some Ideas Survive and Others Die by Chip and Dan Heath and a story about Conrad Hilton. In it there’s this marvelous quote, “The statistics show that people remember stories, not statistics. This has some pretty weird implications if you want valid ideas to spread and stick.”

And that’s really the answer, isn’t it? People say they want the numbers because they like to think of themselves as rational people. But they’re more people than they are rational. What they really want is a story they can believe and remember.