"And each year we discover a few more of those unknown unknowns"

Rediscovered this in some of my earlier writings:

The limitation that ERM faces is captured in the following statement: "There are knowns, known unknowns, and unknown unknowns." (Author unknown.) Former Secretary of Defense Donald Rumsfeld changed this quote as follows: "The message is that there are known knowns—there are things that we know that we know. There are known unknowns—that is to say, there are things that we now know we don't know. But there are unknown unknowns—there are things we do not know we don't know. And each year we discover a few more of those unknown unknowns." (From a briefing by former Secretary of Defense Donald Rumsfeld, as reported in the Daily Telegraph (London), March 12, 2003, at 14.)