I think I know...

Somebody mentioned that quote from Donald Rumsfeld the other day - you know the one, about known knowns, known unknowns and unknown unknowns. And I got to thinking - can you have an unknown unknown? Can there be things which you don't know you don't know? As far as I can make out only a third party can make such a statement. I could say "This person does not know about the Theory of Relativity. Further, they don't know that such a theory exists, and therefore don't know that they don't know about it". So from my perspective, that is an unknown unknown for that person. But as far as the person is concerned, they cannot not know they don't know about it, until they know about it! Only then, in retrospect, can they say "Ah yes, there was that period when I didn't know I didn't know about it". And my head hurts!