“As we know, there are known knowns. There are things we know we know. We also know there are known unknowns. That is to say we know there are some things we do not know. But there are also unknown unknowns, the ones we don’t know we don’t know.” So spoke Donald Rumsfeld, U.S. Secretary of Defense, back in 2002, regarding our knowledge of Saddam Hussein’s Iraq. He could have been talking about Judo, too.