For the butterfly, mating and propagation involve the sacrifice of life, for the human being, the sacrifice of beauty.

One is led astray alike by sympathy and coldness, by praise and by blame

Self knowledge is best learned not by contemplation, but by action.

Everything factual is, in a sense, theory. The blue of the sky exhibits the basic laws of chromatics. There is no sense in looking for something behind phenomena: they are theory.

Do not, I beg you, look for anything behind phenomena. They are themselves their own lesson.

All professional men are handicapped by not being allowed to ignore things which are useless.

Love and desire are the spirit's wings to great deeds.