Then-U.S. Secretary of Defense Donald Rumsfeld made the following statement at a Defense Department briefing in February 2002:
Reports that say that something hasn’t happened are always interesting to me, because as we know, 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.
He was talking about known unknowns that we know about and known unknowns that we don’t know about and the unknown unknowns that we don’t know we know. :mrgreen: