“I know nothing except the fact of my ignorance”- Socrates
“Knowledge itself is power”- Frances Bacon
“The years teach you much which the days never know”- Emerson
“An intellectual is someone whose mind watches itself”- Albert Camus
“It is much easier to make measurements than to know exactly what you are measuring”
-J.W.N. Sullivan
Journals Of Enreal 
This is one of my favorites:
It is impossible for a man to learn what he thinks he already knows. – Epictetus
“Nothing is worse than active ignorance.” -Goethe
There is, to be sure, a profound illusion that first saw the light of the world in the person of Socrates: the unshakable faith that thought, using the thread of logic, can penetrate the deepest abysses of being, and that thought is capable not only of knowing being but even of correcting it. This sublime metaphysical illusion accompanies science as an instinct and leads science again and again to its limits at which it must turn into art—which is really the aim of this mechanism. Nietzsche