Rotten wood cannot be carved.

There are three sorts of pleasures which are advantageous, and three which are injurious. Finding pleasure in the discriminating study of ceremonies and music, finding pleasure in discussing the good points in the conduct of others, and finding pleasure in having many wise friends, these are advantageous. But finding pleasure in profligate enjoyments, finding pleasure in idle gadding about, and finding pleasure in feasting, these are injurious.

Every truth has four corners: as a teacher I give you one corner, and it is for you to find the other three.

Don't make to others what you don't want them to make to you.

When you know a thing, to hold that you know it, and when you do not know a thing, to allow that you do not know it - this is knowledge.

The Master said, “The gentleman understands what is right, whereas the petty man understands profit.” (Analects 4.16)

If a man takes no thought about what is distant, he will find sorrow near at hand.