"There are known knowns; 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…"
That’s former Secretary of Defense Donald Rumsfeld, talking about what we know and don’t know, with regard to weapons of mass destruction. But when it comes to the secretary himself, what do we know?