Rotten wood cannot be carved (朽木难雕)|朽木难雕

朽木难雕
Xiǔ mù nán diāo

Translation: Rotten wood cannot be carved.
Meaning: Something that is already bad cannot be made better, or prettier. You cannot change the true nature of such things. An English equivalent would be: “You can’t teach an old dog new tricks.”

Story
Confucius had a student named Zai Yu, who had a way with words. At first Confucius thought that he could be a very promising student. Before long, however, Zai Yu revealed his true colors: He hated to study.
One day, while Confucius was lecturing, he caught Zai Yu sleeping. His fellow students couldn’t help bursting into a guffaw when they saw him sleep like the dead under the nose of their teacher. Confucius was not amused, but felt sad. Quieting his students down, he said to them, “A piece of rotten wood cannot be carved; a wall of manure and dirt cannot be whitewashed. Zai Yu is a person whose action does not match his words. From him I’ve learned a lesson: Not only should I judge a person by what he says, but also by what he does.”

Vocabulary

Examples
我们的儿子并不喜欢读书，不管我们骂他，打他都没有用，真是朽木难雕。
Our son really doesn’t like studying. We can scold him or hit him, it is all no use; rotten wood cannot be carved.