Book 3, section 4

Don't waste the rest of your time here worrying about other people—unless it affects the common good. It will keep you from doing anything useful. You'll be too preoccupied with what so-and-so is doing, and why, and what they're saying, and what they're thinking, and what they're up to, and all the other things that throw you off and keep you from focusing on your own mind.

You need to avoid certain things in your train of thought: everything random, everything irrelevant. And certainly everything self-important or malicious. You need to get used to winnowing your thoughts, so that if someone says, “What are you thinking about?” you can respond at once (and truthfully) that you are thinking this or thinking that. And it would be obvious at once from your answer that your thoughts were straightforward and considerate ones—the thoughts of an unselfish person, one unconcerned with pleasure and with sensual indulgence generally, with squabbling, with slander and envy, or anything else you'd be ashamed to be caught thinking.

Someone like that—someone who refuses to put off joining the elect—is a kind of priest, a servant of the gods, in touch with what is within him and what keeps a person undefiled by pleasures, invulnerable to any pain, untouched by arrogance, unaffected by meanness, an athlete in the greatest of all contests—the struggle not to be overwhelmed by anything that happens. With what leaves us dyed indelibly by justice, welcoming wholeheartedly whatever comes—whatever we're assigned—not worrying too often, or with any selfish motive, about what other people say. Or do, or think.

He does only what is his to do, and considers constantly what the world has in store for him—doing his best, and trusting that all is for the best. For we carry our fate with us—and it carries us.

He keeps in mind that all rational things are related, and that to care for all human beings is part of being human. Which doesn't mean we have to share their opinions. We should listen only to those whose lives conform to nature. And the others? He bears in mind what sort of people they are—both at home and abroad, by night as well as day—and who they spend their time with. And he cares nothing for their praise—men who can't even meet their own standards.