Piercing one’s shield with one’s spear.

Piercing one’s shield with one’s spear. — One of the meanings of this proverb could be… Self-contradiction. The story about this is that a man was selling shields and spears at a marketplace. He raised up one of his spears and shouted, “This spear can pierce through any wall!” Then, he raised up one of his shields and shouted, “This shield can deflect anything.” When he was asked what would happen if he pierced his own shield with his own spear, he was speechless, since he had contradicted himself. (This is a rough translation from a Chinese proverb)