Self-contradictory
　　There was a person who sold shields and spears. While praising his shields he said: "These shields are so sturdily built that nothing can pierce them." A little later he praised his spears: "My spears are so sharp that they can pierce through anything." Someone asked him: "What if I hit one of your shields with one of your own spears?" The man had no answer to that, because what he said is self-contradictory.

NOTES：
The Chinese characters 矛for "spear" and 盾 for "shield" together form a compound 矛盾(máo dùn) meaning "to contradict", "contradiction" or "contradictory".
自(zì)：self.
相(xiāng)：each other.