3.12.1
We ought not to make our exercises consist in means contrary to nature and adapted to cause admiration, for if we do so, we who call ourselves philosophers, shall not differ at all from jugglers. For it is difficult even to walk on a rope; and not only difficult, but it is also dangerous. Ought we for this reason to practise walking on a rope, or setting up a palm tree, or embracing statues? By no means. Every thing which is difficult and dangerous is not suitable for practice; but that is suitable which conduces to the working out of that which is proposed to us. And what is that which is proposed to us as a thing to be worked out? To live with desire and aversion (avoidance of certain things) free from restraint. And what is this? Neither to be disappointed in that which you desire, nor to fall into any thing which you would avoid. Towards this object then exercise (practice) ought to tend. For since it is not possible to have your desire not disappointed and your aversion free from falling into that which you would avoid, without great and constant practice, you must know that if you allow your desire and aversion to turn to things which are not within the power of the will, you will neither have your desire capable of attaining your object, nor your aversion free from the power of avoiding that which you would avoid. And since strong habit leads (prevails), and we are accustomed to employ desire and aversion only to things which are not within the power of our will, we ought to oppose to this habit a contrary habit, and where there is great slipperiness in the appearances, there to oppose the habit of exercise.