Mens sana in corpore sano -- "sound in mind, sound in body" -- is a piece of perennial wisdom. It comes to us from the Roman poet Juvenal but has roots in the culture and philosophy of ancient Greece. In America, it was once such common sense that a sneaker manufacturer turned it into a brand slogan. Virtue ethics, one of the three main branches of ethics, is also inherited from the ancient Greeks. Virtue ethics is concerned with how or what kind of person one should be. It aims to cultivate human excellence through self-conscious mastery of habit.