The four rules of Toyota's lean production site management are as follows:
Rule 1: The content, sequence, time and results of all work must be clearly defined.
Rule 2: Every customer-supplier relationship must be direct, and the way to send a request and get a response must be clear and correct, either "yes" or "no".
Rule 3: The circulation route of each product and service must be simple and direct.
Rule 4: All improvements must be made at the lowest possible organizational level under the guidance of teachers and in accordance with scientific methods. These four rules require that all kinds of operations, connections and process routes of enterprises must be able to carry out self-inspection to automatically issue early warning of problems. It is precisely because of the constant response to the problem that the seemingly rigid system can remain flexible and adapt to the changing environment.