“There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things we know we don’t know. But there are also unknown unknowns. There are things we don’t know we don’t know.”
It is one of the most derided quotes of all time: simultaneously mocked both for its obviousness and its obscurity, Donald Rumsfeld was trying – ham-fistedly – to explain US foreign policy in Iraq. And we know how well that turned out.