Based on a new study reported by the NYT, people who do things badly

are usually supremely confident of their abilities -- more confident, in fact, than people who do things well.

Humor-impaired joke-tellers rated themselves as funny . . .

One reason that the ignorant also tend to be the blissfully self-assured, the researchers believe, is that the skills required for competence often are the same skills necessary to recognize competence.

It would seem, then, that you shouldn't ever ask someone whether they are good at what they do. This is a good reason to downplay the importance of oral interviews.