Past Experience, If Not Forgotten, Is a Guide for the Future.
This concept is meant to remind people of the need to learn from past experience and make it a guide for the future. In ancient China great importance was attached to writing history and thus historiography experienced great progress. It was so designed as to review the successes and failures of previous dynasties and recount the good and evil in historical figures, especially sovereigns and officials, in order to provide a warning or a guide for the future.
In observing past events and learning of ancient times, I have found that the good things in the world are always the same, but it has never occurred that when a sovereign and his officials have had equal power, they can still live harmoniously. We should not forget past experience, but instead use it as a guide for the future. (Strategies of the Warring States)
I have heard that past events are a guide to future events and that the words and actions of ancient people provide models for people of the present age. Even though time has changed, they are not off the mark in providing criteria for right and wrong. (Zhao Pu: Memorial Urging Emperor Taizong to Withdraw Troops)