"All theory, dear friend, is gray, but the golden tree of life springs ever green."

"The highest happiness of man is to have found out what he is to do, and to do it."

"The truly wise man is he who knows that he knows nothing."

"A man can stand anything except a succession of ordinary days."

"The human race is a monotonous affair. What one does, the other does, and what one suffers, the other suffers."