"There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there

"There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know." - Donald Rumsfeld