Bk. III. 4.
Do not waste the time you have left in life thinking about what others are thinking when you could be thinking about something useful. You are losing the chance to think about something besides “what is so-and-so doing? and why? What is so-and-so saying? What is so-and-so thinking? What is so-and-so plotting?”
All this takes us away from watching our own minds.
We must watch our thoughts, noticing useless thoughts, especially malignant thoughts and over-thinking. We must strive to think in such a way that, should we stop and ask, “What am I thinking right now?” we can always answer immediately, “this,” “that,” and every thought is simple and benevolent—the kind of thought that befits a social animal—not indulgences or back-biting or envy or suspicion or anything else that would make us blush.
For those who seek to be among the best of humanity, those accessing the deep good within, strive to be uncontaminated by indulgence and untouched by insult, feeling no wrongs, That one is a fighter in the noblest fight; one who cannot be overcome by passions. That one is deep-dyed in justice, accepting what happens and not worried about the opinions of others. Then it is only our actions that concern us and we are content where we are, for where we are is where are are coming from.
These remember that all living things are our family and that caring for all is our nature and that we should worry about the opinions only of those who live according to the natural way of things.
But as for those who do not live according to nature, we keep in mind what they are and what they do, and we do not worry about the opinions of those who do not value themselves.