Donald Rumsfeld on Known Knowns and Unknown Unknowns

Reports that say there's-- that, that, 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.