Aristotle's "Nicomachean Ethics" is considered to be one of the most important treatises on ethics ever written. In an incredibly detailed study of virtue and vice in man, Aristotle examines one of the most central themes to man, the nature of goodness itself. In Aristotle's "Nicomachean Ethics," he asserts that virtue is essential to happiness and that man must live in accordance with the "doctrine of the mean" (the balance between excess and deficiency) to achieve such happiness.