“The gem cannot be polished without friction, nor man perfected without trials.”

“Real knowledge is to know the extent of one's ignorance.”

“The wound is the place where the light enters you.”

“The only true wisdom is in knowing you know nothing.”

“Learning never exhausts the mind.”

“He who has a why to live can bear almost any how.”

“An investment in knowledge pays the best interest.”

“Whatever you are, be a good one.”