Rumsfeld stated: Reports that say 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. ... But there are also unknown unknowns—the ones we don't know we don't know.

What is unknown knowledge?

Known knowns, unknown knowns and unknown unknowns

That is to say there are things that we now know we don't know. ... Known knowns — things that we know (i.e are aware of) that we know. These pose less of a risk, as they are facts we are confident in.

What are unknown unknowns examples?

Unknown unknowns: Things you're neither aware of nor understand (examples: starting a business or taking a sabbatical)