Knowns & Unknowns (Or Ujloijlkjnowifhnjgno)

As we know
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.
But there are also unknown unknowns,
The ones we don't know
We don't know.

Prof Frank Cowell quotes Donald Rumsfeld in a Department of Defense news briefing on 12 Feb 2002 to start off the chapter on 'Information' in Microeconomics.

What an encouraging opening to the chapter...!