Common sense and science tell us that if an assertion is correct, no matter how you analyze and reason, you will never come to a wrong conclusion; On the contrary, it is the same. Thus, as early as 2000 years ago in ancient Greece, people discovered such a contradiction: these two "theorems" were proved by recognized correct reasoning methods, and if one of them was admitted to be correct, the other would be inferred to be wrong. There is even a proposition that if it is admitted to be correct, it can be inferred that it is wrong; If you admit that it is incorrect, you can infer that it is correct.

This kind of thing seems absurd, but it actually exists objectively. Scientists call this phenomenon "paradox". Today, although mathematicians can't reasonably explain the paradox, it is with the efforts of this explanation that mathematicians have made a series of discoveries, which have led to the establishment of a large number of new disciplines and promoted the development of mathematical science. Paradox also reflects that rigorous mathematical science is not monolithic, and there are many contradictions in its concepts and principles. Mathematics is gradually developed and perfected in solving contradictions. The existence of paradox also tells people that when studying and studying mathematics, we must keep in mind the famous saying of ancient Greek mathematicians: we must doubt everything, and only in this way can we find something.