“These are the things we know that we know. “There are known unknowns. That is to say, there are things that we know we don’t know,” Rumsfeld continued. “But there are also unknown unknown ...

Former US Secretary of Defense Donald Rumsfeld famously talked about "known knowns" (things we know we know), "known unknowns" (things we know we don't know), and "unknown unknowns" (the things we ...

the late Donald Rumsfeld, 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.