Honesty and the ability to own up to your mistakes. It can also show arrogance depending on their response.
One candidate we interviewed answered my question saying that he had never made a mistake like that. Then he went on to tell me a story about how a bad patch from Oracle which he applied brought down production this one time.
The guy seemed arrogant, and I felt like he was lying or he is overstating his skills. Either way, he ended up getting hired by another team (knowing full well that we didn't like him), and he only stayed for about a month or two.
Go figure.