Aristotle, Nicomachean Ethics
H. Rackham, Ed.

and pain in general, either too much or too little, and in both cases wrongly; [11] whereas to feel these feelings at the right time, on the right occasion, towards the right people, for the right purpose and in the right manner, is to feel the best amount of them, which is the mean amount—and the best amount is of course the mark of virtue. [12] And similarly there can be excess, deficiency, and the due mean in actions. Now feelings and actions are the objects with which virtue is concerned; and in feelings and actions excess and deficiency are errors, while the mean amount is praised, and constitutes success; and to be praised and to be successful are both marks of virtue. [13] Virtue, therefore is a mean state in the sense that it is able to hit the mean. [14] Again, error is multiform （for evil is a form of the unlimited, as in the old Pythagorean imagery,¹ and good of the limited）, whereas success is possible in one way only （which is why it is easy to fail and difficult to succeed—easy to miss the target and difficult to hit it）; so this is another reason why excess and deficiency are a mark of vice, and observance of the mean a mark of virtue:

Goodness is simple, badness manifold.² [15]

Virtue then is a settled disposition of the mind determining the choice³ of actions and emotions, consisting essentially in the observance of the mean relative to us,