9/11 Live: The NORAD Tapes

"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.Secretary of Defense Donald Rumsfeld, 12 Feb 2002
 
(image by the Black Rose)