The former US defence secretary famously articulated on February 12, 2002, that “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”. Though Rumsfeld’s words were in response to a query about the complete absence of evidence linking Saddam Hussein’s regime in Iraq to the supply of “weapons of mass destruction” to various terrorist groups. Though this remark earned him...