I know this was a thread in the old forums, and I couldn't find it around here ...If there is one, please delete.
Here is a memorable quote that I do really like ... It is a thinking person's quote ...
"There are known knowns. There are things we know that we know. There are known unknowns. That is to say, there are things that we now know we donít know. But there are also unknown unknowns. There are things we do not know we donít know."