The Zhongyong, one of the Four Books, teaches that before emotions arise the mind is in equilibrium, and when they arise in due measure there is harmony. It identifies sincerity, cheng, as the way of heaven, and the sage as one who, being sincere, forms a triad with heaven and earth.
Zhongyong
The Doctrine of the Mean: a Confucian classic on balance, harmony and sincerity.
Also: Doctrine of the Mean, Centrality and Commonality