There are unknown unknowns

"There are unknown unknowns" is a phrase from a response United States Secretary of Defense Donald Rumsfeld gave to a question at a U.S. Department of Defense (DoD) news briefing on February 12, 2002, about the lack of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups. 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.

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