I describe research at the intersection of cognitive and social psychology investigating how accurately people evaluate their intellectual, professional, and social performances—a task not only at the heart of meta-cognition but also the ancient Western exhortation to “know thyself.” In particular, I discuss the so-called Dunning-Kruger effect, which asserts that inexpert and unknowledgeable individuals fail to recognize (scratch that, cannot be expected to recognize) just how severe their deficits are. I discuss the mechanisms underlying the effect, and also its social cognitive extension: People in general not only have difficulty identifying intellectual weaknesses in themselves but also genius and virtuosity in other people.