This idiom is rooted to an interesting old story and is still widely used in today’s daily life.
Once upon a time, a man in the state of Chu had a spear and a shield for sale. He loudly praised his spear and shield. Very soon, a big crowd gathered around him.
“Look,” said the man, picking up his shield. He clanged and showed it to the crowd. “My shield is very strong. Nothing in the world, no matter how hard and sharp it may be, can pierce through it.”
With a proud expression on his face, the man put down his shield and picked up his spear. Brandishing his spear, he said, “My spear is the best in the world. It is so strong that it can pierce through anything.”
“Wait a minute,” shouted one of the on-lookers from the crowd, “I wonder if you could tell us what would happen if your spear is used to pierce your shield?”
It is impossible for an impenetrable shield to coexist with a spear that finds nothing impenetrable. The seller was tongue-tied. He did not have an answer and the crowd burst out laughing.
Hence the expression “Zi Xiang Mao Dun” (literally, one’s spear contradicts his/her own shield) is used to mean self-contradiction. Dear readers, do you have done or met anything that “Zi Xiang Mao Dun”?