The era in which the author lived. After the July 7th Incident, all the lights in Tsinghua Library went out. The "real world" refers to the era in which the author lives. Because of the July 7th Incident, the fate of the country is at stake. As an institution for collecting, sorting and collecting books and materials for people to read and refer to, the library appeared as early as 3000 BC. Library has the functions of preserving human cultural heritage, developing information resources and participating in social education.