The greatest amount of knowledge, if it has not been worked over by one’s own thinking, is worth much less than a far smaller amount that has been thoroughly thought through.

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  To estimate how happy a man is, one should ask not what pleases him, but what troubles him.

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  Solitude is the lot of all outstanding minds.

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  What a man is in himself, what accompanies him when he is alone, what no one can give or take away, is more essential to him than everything he has or what he may be in the eyes of others.

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  Bad books are intellectual poison; they destroy the mind.

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  The safest way of not being very miserable is not to expect to be very happy.

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  The wise man aims at freedom from pain, not at pleasure.

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