Donald Rumsfeld was often the butt of cheap jokes after this quote. In reality, Rumsfeld was absolutely spot on and close to philosophic.
Starting from where Rumsfeld left off we come to the distinction between the knowable and the unknowable
These are things we don’t know that we don’t know. There are knowable unknowns. That is to say, there are things that we could know but we don’t know which we don’t know. But there are also unknowable unknowns. There are things we cannot know that we don’t know that we can never know.
a la Rumsfeld
I am coming to the conclusion that the sum of all human cognition lacks some of the dimensions of the universe. It may be increasing with time, but human cognition is limited. The expanding universe may be infinite or it may be boundless. For human cognition to grasp the universe is then like trying to measure an infinite length with a ruler of finite length, or of trying to measure some unknown parameter with a ruler marked in inches. Those measurements will never reach a conclusion.
The k2p blog 