The design of perpetual motion machine violates the laws of nature, and the method of constructing hydropower station by using the unique terrain of the Yangtze River is a product with unique natural conditions and cannot be copied, so it is not practical. Rhinoplasty belongs to the non-therapeutic surgical method of human body or animal body. Because it is realized by living people and cannot be used in industry, it is not practical. Practical requirements can be used in industry, but this does not mean that it must be a large machine industry and can be used in handicraft industry. Robots that can be used in surgery are essentially robots, not data methods of diseases, so they are practical.