To arrive at perfection, a man should have very sincere friends or inveterate enemies; because he would be made sensible of his good or ill conduct, either by the censures of the one or the admonitions of the other.

One original thought is worth a thousand mindless quotings

To become self-educated you should condemn yourself for all those things that you would criticize others.

If you are to be kept right, you must possess either good friends or red-hot enemies. The one will warn you, the other will expose you.

On being asked by someone how he could become famous, Diogenes responded: 'By worrying as little as possible about fame

Even if I am but a pretender to wisdom, that in itself is philosophy.

Of what use is a philosopher who doesn't hurt anybody's feelings?