You don't know what you don't know.

There is no learning without remembering.

All that I know is nothing - I'm not even sure of that.

To know, is to know that you know nothing. That is the meaning of true knowledge.

The only good is knowledge and the only evil is ignorance.

The stomach is the only part of man which can be fully satisfied. The yearning of man's brain for new knowledge and experience and for more pleasant and comfortable surroundings never can be completely met. It is an appetite which cannot be appeased.