The West's "Unknown Knowns"

In Washington recently I met Donald Rumsfeld, America’s former defense secretary. Rumsfeld became almost as famous for his musings about “known unknowns” as he was controversial over his role in the Iraq war.
He is also widely respected for his intellect and his incisive, take-no-prisoners approach to foreign and defense issues. So I wanted to know what he made of a world which has now become infinitely more complex, chaotic and dangerous.