Moderation, which consists in indifference about little things, and in a prudent and well-proportioned zeal about things of importance, can proceed from nothing but true knowledge, which has its foundation in self-acquaintance.
Consider how great is the encouragement which all the world gives to the lover; neither is he supposed to be doing anything dishonourable; but if he succeeds he is praised, and if he fail he is blamed.
True opinions are a fine thing and do all sorts of good so long as they stay in their place; but they will not stay long. They run away from a man's mind, so they are not worth much until you tether them by working out the reason. Once they are tied down, they become knowledge, and are stable.
Remember our words, then, and whatever is your aim let virtue be the condition of the attainment of your aim, and know that without this all possessions and pursuits are dishonourable and evil.