Reason 1: Social resources do not appear out of thin air. The reason why it has been free is because our country's strong financial resources are supporting it. However, such a big country and so many people mean that this is a huge expenditure, which is not a long-term solution after all.

Reason 2: Raise the awareness of crowd mobility. Although the country has repeatedly stressed the harm of the virus and advised people to gather less and move less, repeated outbreaks have shown that there are always some people who turn a deaf ear, and some even knowingly commit crimes, resulting in adverse consequences.

Reason 3: Make epidemic prevention and control more optimized. It is more centralized and easier to manage nucleic acid detection for some floating population.