Once upon a time, there was a merchant from the state of Chu. He wanted to sell his spear and shield, so he set up a stall in a busy market.
He picked up his shield first and shouted loudly, "Come and have a look, everyone. This shield of mine is the toughest shield in the world. No matter how sharp an object is, it can't pierce through it." Hearing this, the people around gathered to look at this amazing shield, and they were all whispering and talking among themselves.
Then, the merchant picked up his spear and said even more proudly, "This spear of mine is the sharpest spear in the world. No matter how tough an object is, it can pierce through it at once." At this time, someone in the crowd raised a question, "What would happen if you use your spear to stab your shield?" The merchant was stunned all of a sudden. He opened his mouth but didn't know how to answer. The people around all burst into laughter, and the merchant blushed with shame.
This story tells us that we should not be self - contradictory in what we say and do. Otherwise, like this merchant, we will be laughed at.