Attack the shield with his spear.

Using the spear of a child as a shield to attack is a metaphor to refute the other party's views, methods or remarks.

During the Warring States Period, the great thinker Han Feizi once said that there was a man who sold spears and shields. Someone told him that his spear is the sharpest spear in the world, and nothing is impenetrable. Later, he sold it to people, saying that his shield was the hardest shield in the world and nothing could pierce it. Someone in the crowd asked him to poke his shield with a spear, so he had to run away.

Because of the attack, human beings made spears first, and because human beings also need to defend themselves from being attacked, they also made shields, and vice versa. Therefore, whether attacking or defending first, spear and shield need to be equally important. When people are testing who has the advantage over spears and shields, they have the idea of attacking their shields with their spears, that is, attacking them with spears and shields.