Aristotle, Nicomachean Ethics
H. Rackham, Ed.

[15] Similarly men suppose it requires no special wisdom to know what is just and what is unjust, because it is not difficult to understand the pronouncements of the law. But the actions prescribed by law are only accidentally just actions. How an action must be performed, how a distribution must be made to be a just action or a just distribution—to know this is a harder task than to know what medical treatment will produce health. Even in medicine, though it is easy to know what honey, wine and hellebore, cautery and surgery are, to know how and to whom and when to apply them so as to effect a cure is no less an undertaking than to be a physician.