An armorer of Chu boldly claims to make the best spears and shields. "My shields are so strong; they cannot be penetrated by any weapon," he said. "My spears are so sharp; they can pierce any shield," he further said.
A man asks, "If your spear is thrown at your shield, what then?"
The armorer had no reply. By logic, both an impenetrable shield and an all-piercing spear can not exist at the same time. State of Chu (841-233 BCE), Zhou Dynasty, China
