"Reports that say something hasn't happened are interesting to me, because as we know, there are known unknowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know."
Donald 'pass the crack pipe' Rumsfeld

Yeah, but you forgot unknown knowns, when you know something but just don't know you know. You know?