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

"To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge."
— Nicolaus Copernicus

Results! Why, man, I have gotten a lot of results. I know several thousand things that won't work.
-- Thomas Edison

Knowledge is a comfortable and necessary retreat and shelter for us in an advanced age; and if we do not plant it while young, it will give us no shade when we grow old.
-- Lord Chesterfield

You'll feel terribly sad when you are old if not try hard to learn when you were young.
-- Chinese Proverb.

Every great advance in natural knowledge has involved the absolute rejection of authority.
--- Thomas Huxley

Knowing it and applying it are two different things.

Ignorance doesn't kill you, but it makes you sweat a lot. 
--  Haitian proverb