Just in case you’d forgotten, here’s good old Donald Rumsfeld with his known unknowns.
Or Slate has expressed it more poetically:
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
Oh, the horror, the horror as gobbledegook (albeit true, but gobbledegook nonetheless) best left in the M.B.A. seminar room escapes out into the real world!
As for me, I’ll go with Mark Twain (or IS it Mark Twain? I don’t know for sure….)
It ain’t what you don’t know that gets you into trouble; it’s what you know for sure that just ain’t so.
A good little aphorism for life in general, and especially for historians, I reckon.