"From the individual to the general" is the application of generalization and abstract thinking in mathematics. Mathematics is an abstract subject, which comes from the generalization and abstraction of the real physical world. Therefore, there is no one-to-one correspondence between the mathematical world and the physical world, that is to say, some theories exist only in mathematics, but cannot be applied in the physical world, such as the theory of dividing the ball, which is the so-called Barnah-Talsky paradox.