Wisdom from the Early Stoics, Zeno of Citium 57

By the nature with which our life ought to be in accord, Chrysippus understands both Universal Nature and more particularly the nature of man, whereas Cleanthes takes the Nature of the Universe alone as that which should be followed, without adding the nature of the individual. 

And virtue, he holds, is a harmonious disposition, choice-worthy for its own sake and not from hope or fear or any external motive. 

Moreover, it is in virtue that happiness consists; for virtue is the state of mind which tends to make the whole of life harmonious. 

When a rational being is perverted, this is due to the deceptiveness of external pursuits or sometimes to the influence of associates. For the starting-points of nature are never perverse. 

—Diogenes Laërtius, 7.89