He was ridiculed for talking about "unknown unknowns" because of the ridiculous phrasing. See http://www.youtube.com/watch?v=GiPe1OiKQuk
Interestingly, this ridicule became so common that now people know more about known unknowns, and unknown unknows, which is perfectly sound logic, but just weirdly associated with Rumsfeld now.
I'm no Rumsfeld fan, but I never understood why that statement would be ridiculed. The quote below makes perfect sense to me.
"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. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones."
Yeah that statement also made sense to me despite not liking the guy. I like to think of "known unknowns" as knowing the question but not the answer, and "unknown unknowns" as not even knowing the question.
Of course knowing the answer but not the question is best left to Douglas Adams.
Yeah, I always found that ridicule odd. I'm no fan of the guy but it was a perfectly good point (and, in fact, was disastrously proven true pretty quickly).
