The governments of ancient sage emperors had systems that recorded errors and mistakes committed by previous rulers； and court musicians sang adages and aphorisms to remind emperors of the righteous ways of governing. Ordinary folks could be heard muttering complaints on rulers by the roadside, businessmen and travelers were talking about the government's wrong policies and faulty actions in the marketplace. Then the  Emperors heard all the comments and were quick to rectify mistakes, and to follow whatever suggestions that are right and justified. That's why they enjoyed longevity of their monarchies. --《Han Shu》 Vol. 5