KD 17 Ὁ δίκαιος ἀταρακτότατος, ὁ δ’ ἄδικος πλείστης ταραχῆς γέμων.
One who is just, moral, and virtuous has peace of mind; but one who is unjust and amoral is overflowing with agitation, confusion, and uncertainty. (Translation is my own)(ταραχῆς, i.e., the opposite of αταραξία).
This Principal Doctrine just makes sense. If you are just in your dealings with other people, moral in your actions, and do your best to display fair behavior, you have no need to be troubled. You've done your best. Don't get me wrong. Bad things will happen to you, and some people still won't like you. But you don't control that. Your mind can be at peace. On the other hand, if you treat people poorly, display amoral behavior, and are basically an objectively poor excuse for a human being, you have reason to be troubled! People will be out to get you. If you're the latter, you need to have some frank speech with yourself and get on the right track. To paraphrase Wil Wheaton: Don't be a jerk! If you take his advice and the advice of this Doctrine, you and all of us who interact with you will be the better for it.