Rumsfield:
"Reports that say something hasn't happened are 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."

拉姆斯菲尔德著名语录: 知知、知不知、不知不知
“我总是对有关找不到伊拉克大规模杀伤性武器的报道很感兴趣，因为我们知道，世界上存在着已知的已知事物，也就是说有些事情我们知道自己知道，而我们也知道世上存在着被人所知的不明事物，这就是说有些事情我们知道自己不知道。同时，世上还存在着我们不知道的不明事物，也就是说我们不知道自己不知道。” -2003年2月。