The Known Unknowns

Much better when you hear it recited, but, forthwith, a bit of poetry by Donald Rumsfeld, from the Slate piece by Hart Seely:

The Unknown

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.

—Feb. 12, 2002, Department of Defense news briefing