
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. (ang.)
wypowiedź podczas briefingu prasowego 12 lutego 2002.
Źródło: „Świat Nauki” http://www.swiatnauki.pl/?q=art&n=200510b