Andy Lester - What's the worst bug you've ever written?:

"Then, after the candidate tells me the story of the terrible bug, I ask the crucial follow-up: "What did you learn? What did you change about yourself?" The reaction is often telling, and I can easily see how self-aware she is. If the answer is "We fixed the bug and had to do some cleanup," then I know nothing's been learned. If she comes back with a "I'll tell you one thing: I made sure that my X always....", I know that she's a self-optimizing person."