And we don't know what we don't know, Senator.
Rumsfeld
The context is that he'd previously said we had to invade Iraq because of the imminent threat of the weapons of mass destruction.
So he's using a trivially true and non-interesting statement about "unknown unknowns" to evade questions about previous statements where he claimed to know something.
In other words, it was garbage response. He deserves mockery, scorn and a criminal trial.
I’m not sure that’s quite accurate, although it’s not that far off either. The full context is here:
https://web.archive.org/web/20160406235718/http://archive.de...
His “unknown unknowns” response was, to me, a basically fair if evasive response to whether there is any evidence of a direct link between Baghdad and terrorists as far as supplying WMDs. He essentially said “we don’t know what we don’t know.”
To me the more damning answer is the follow up later in the conference, where he strongly implied that he has evidence but can’t disclose it. That just misled the public and is far worse than the “unknown unknowns” comment in my view.