Meditations by Marcus Aurelius Book 7 Page 29

constitution, is, that he intend the common good. The second is, that he yield not to any lusts and motions of the flesh. For it is the part and privilege of the reasonable and intellective faculty, that she can so bound herself, as that neither the sensitive, nor the appetitive faculties, may not anyways prevail upon her. For both these are brutish. And therefore over both she challengeth mastery, and cannot anyways endure, if in her right temper, to be subject unto either.

And this indeed most justly. For by nature she was ordained to command all in the body. The third thing proper to man by his constitution, is, to avoid all rashness and precipitancy; and not to be subject to error. To these things then, let the mind apply herself and go straight on, without any distraction about other things, and she hath her end, and by consequent her happiness.