As a  proverb goes: "Never forget past experiences, they are guides for the future." When men of noble character rule the country, they study the historical lessons of ancient times, and test them in the present society, especially in managing human relations, ing the reasons for ancient countries' prosperity or decline, seeking the best ways to govern, choosing the best opportunity to advance or to retreat. All changes are done orderly and timely.  Therefore the nation will be stable and the people enjoy peaceful life for a long time.