"The title derives from a frequently parodied Rumsfeld response to a reporter's question about whether there actually was evidence of any link between Saddam Hussein and terrorists seeking weapons of mass destruction. The Defense secretary responded: "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. 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." Tim Rutten, LA Times.