Once upon a time, in the Kingdom of Chu of China, there was a man who sells shield and spears. Well, it is understandable that sellers always praise what they are selling. This man bragged about the high quality of his products. He says to others: my shields are the strongest one on the world, no sharp things can penetrate it. And then he takes one of his spears and boasts: my spear is the sharpest spear, no matter how strong an item is, it can penetrate it.
Upon hearing this, one person asks him: well, you said your shield is
the strongest and your spear is the sharpest, then I have a question, what if when you use your spear to attack your shield? This seller can’t answer the question and is speechless.
The shield that can’t be broken and the spear that can penetrate everything can’t exist in the world simultaneously. In one judgment question, one can’t make two opposite judgments. If doing so, then he or she makes a logic mistake. Contradictions exist commonly in the world. Everything has contradictions, no matter in the material world or in the intellectual world. Contradictions are not bad things. The most important thing is to realize them and solve the conflicts, only in this way, can things develop.