What does "Selling Sheep" tell us?

The idiot sells sheep. During the Liang Dynasty, there was a scholar who was mentally demented and did not know how to recognize sheep. Once, someone gave him a ram. He tied the sheep's neck with a rope and took it to the market to sell. Others offered very low prices, and even after selling for a long time, no transaction was completed. People in the market knew that he was crazy, so they secretly exchanged a macaque for the sheep. When the scholar saw the macaque, he thought it was a sheep. The strange macaque suddenly changed its appearance and lost its horns. I also looked at the macaque's hands and feet that kept moving, so I thought someone in the market had twisted its horns, but since there were no scars on the monkey's head, I couldn't blame anyone else. So he led the macaque home and chanted: "I have a strange beast that can be fat or thin. First it smelled like sheep. Now it smells bad. I took it to the market several times, but it couldn't be sold three times. It lost both horns on its head and its face. It turns into orange peel and wrinkles."

This is an ancient joke. It doesn't have a big meaning. It is a story about a fool who doesn't know that a sheep has been stolen and still justifies it.