“There must be new materials and new problems in the learning of an era. It is a new academic trend in this era to use this material to study problems. Among those who study knowledge, those who can follow this trend say that they are the mainstream. Those who fail to follow the trend are said to be out of fashion. This is the universal meaning of ancient and modern academic history, this is the general truth of the ancient and modern academic history, which is not those who make things behind closed doors can understand.”