Full Idea
The first prerequisite for knowing anything is the knowledge that we do not know.
Gist of Idea
To learn something, you must know that you don't know
Source
Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884], Intro)
Book Reference
Frege,Gottlob: 'The Foundations of Arithmetic (Austin)', ed/tr. Austin,J.L. [Blackwell 1980], p.-9
A Reaction
This is serious practical advice for teachers. Intelligent people are aware of most philosophical problems, but tongue-tied when asked to discuss them.