Slavoj Zizek even took this quote up, and made the point that there is a fourth category, the “unknown knowns” - the beliefs and values and etc. that we act upon as if they are truth without being aware that they exist. Or as he put it, “the disavowed beliefs, suppositions, and obscene practices we pretend not to know about, although they form the background of our public values.”
Frankly, the whole set of constructs has been tremendously helpful to me in teaching therapists and counselors; I find myself quoting Rumsfeld rather often in fact.
