Who knows the fable of "spear and shield"

A Chu man selling shields and spears boasted that his shield was so strong that nothing sharp could penetrate it. He also boasted that his spear was so sharp that any solid could pierce it. Someone asked him, "What would happen if you stabbed your shield with your spear?" Men are speechless.

An impenetrable shield and a spear that pierces everything cannot exist at the same time. It is impossible for a person to make diametrically opposite judgments on the same question in the same judgment. If he does this, he will make a logical mistake. Contradiction is the universal form of things, everything has contradictions, whether it is the objective world of matter or the subjective world of thinking, there is an arrogant problem.

Contradictions are not necessarily a bad thing. Only when there are contradictions can things progress and develop. The key is to understand contradictions, analyze contradictions, study contradictions and solve contradictions. Only in this way can things develop.