The wisdom to know the difference

Most people know the Serenity Prayer in which we ask for the serenity to accept the things we cannot change, the courage to change the things we can, and the wisdom to know the difference. That is what the philospher Epictetus is talking about at the very beginning of his Enchiridion, or Manual:

Of things, some are in our power and others are not. In our power are opinion, movement towards a thing, desire, turning from a thing; and in a word, whatever are our own acts. Not in our power are the body, property, reputation, offices (magisterial power), and in a word, whatever are not our own acts. And the things in our power are by nature free, not subject to restraint nor hindrance: but the things not in our power are weak, slavish, subject to restraint, in the power of others. Remember then that if you think the things which are slavish by nature to be free, and the things which are in the power of others to be your own, you will be hindered, you will lament, you will be disturbed, you will blame both gods and humans: but if you think that only which is your own to be your own, and if you think that what is another's as it really is, belongs to another, no one will ever compel you, no one will hinder you, you will never blame any person, you will accuse no person, you will do nothing involuntarily (against your will), no person will harm you, you will have no enemy, for you will not suffer any harm.

This is not saying that bad things will not happen. It is saying you will not interpret something that is not in your power to be ultimately harmful. This is a philosophy that makes a person spiritually invincible no matter what another person says or does -- no matter what might happen through nature.