Contradiction in Chinese

contradiction: 矛盾
[English] spear and shield
原文：楚人有鬻盾与矛者，誉之曰：“吾盾之坚，物莫能陷之。”以誉其矛曰：“吾矛之利，于物无不陷也。”或曰：“以子之矛陷子之盾，何如？”其人弗能应也。夫不可陷之盾与无不陷之矛不可同世而立。
[English] A salesman selling shields and spears boasts: "my shield is so strong so that nothing can pierce through it." In the meantime, he continues: "my spear is incomparably sharp since nothing withholds its attack." Someone questions: "what will happen then if your spear is thrust at your shield?" The salesman closes his mouth and can not come up with a answer. The simple truth is that an impenetrable shield does not coexist with a pierce-all spear.