“This must be noted, that it is the nature of such things to be spoiled by defect and excess; as we see in the case of health and strength (since for the illustration of things which cannot be seen we must use those that can), for excessive training impairs the strength as well as deficient: meat and drink, in like manner, in too great or too small quantities, impair the health: while in due proportion they cause, increase, and preserve it.
“Thus it is therefore with the habits of perfected Self-Mastery and Courage and the rest of the Virtues: for the man who flies from and fears all things, and never stands up against anything, comes to be a coward; and he who fears nothing, but goes at everything, comes to be rash. In like manner too, he that tastes of every pleasure and abstains from none comes to lose all self-control; while he who avoids all, as do the dull and clownish, comes as it were to lose his faculties of perception: that is to say, the habits of perfected Self-Mastery and Courage are spoiled by the excess and defect, but by the mean state are preserved.
“Furthermore, not only do the origination, growth, and marring of the habits come from and by the same circumstances, but also the acts of working after the habits are formed will be exercised on the same: for so it is also with those other things which are more directly matters of sight, strength for instance: for this comes by taking plenty of food and doing plenty of work, and the man who has attained strength is best able to do these: and so it is with the Virtues, for not only do we by abstaining from pleasures come to be perfected in Self-Mastery, but when we have come to be so we can best abstain from them: similarly too with Courage: for it is by accustoming ourselves to despise objects of fear and stand up against them that we come to be brave; and after we have come to be so we shall be best able to stand up against such objects.
“And for a test of the formation of the habits we must take the pleasure or pain which succeeds the acts; for he is perfected in Self-Mastery who not only abstains from the bodily pleasures but is glad to do so; whereas he who abstains but is sorry to do it has not Self-Mastery: he again is brave who stands up against danger, either with positive pleasure or at least without any pain; whereas he who does it with pain is not brave.
“For Moral Virtue has for its object-matter pleasures and pains, because by reason of pleasure we do what is bad, and by reason of pain decline doing what is right (for which cause, as Plato observes, men should have been trained straight from their childhood to receive pleasure and pain from proper objects, for this is the right education).” — Aristotle, The Ethics (ed. Smith)