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Popularized by Donald Rumsfeld in 2002, though used much earlier.
- An uncertainty of unknown magnitude, consequence, structure, and probability characteristics, possibly with completely unsuspected existence; something that we don't know that we don't know.
- 1970, United States Congress. Senate. Committee on the Judiciary. Subcommittee on Antitrust and Monopoly, Competition in Defense Procurement – 1969: Hearing, Ninety-first Congress, page 166:
- This means there are technical unknowns, unknown unknowns, and technical uncertainties in the contract.