According to the Stoics, people act according to their impressions. What does that mean? It means that when some event happens (it may just happen or the event may happen specifically to us as an individual) we may react a few different ways.
We may react instinctively, without thinking. Or maybe we simply observe the event - like watching a leaf fall from a tree. Or maybe we acknowledge the event and consider what it has to do with us. If we are required to have an opinion, we may think about it and decide. If no opinion is required, perhaps we simply pass. And on that last part - what criteria should we use if we are to have an opinion?
For many people, events impress themselves upon us and we allow ourselves to react without thinking. You're reading a book in a quiet room. A little girl enters the room and begins whistling. It bothers you and you instinctively yell at her. There was no wrong done on her part. 'But she should see that I'm reading and I need quiet!' Fine, then teach her and try to persuade her why she should not be whistling in the room right now.
This is a dumb little example, but it is a microcosm of the greater world. People may think that being angry is a virtue. And until you can convince them otherwise, why should they not go on living angrily? Either bear (have patience with) what others do, or make a genuine attempt to convince them of the better way. But no grumbling and complaining.
Epictetus runs through a similar scenario with Medea (see this summary of her). He succinctly states that Medea thinks it is better to gratify her anger toward her husband than to protect her children. Most of us would see this as folly! To which Epictetus says, "Show her clearly that she is mistaken and she won't follow that course; but as long as you haven't shown it, what else can she do than follow what seems best to her? Nothing else. Why should you be angry with her, then, because, poor wretch, she has gone astray on matters of the highest importance, and has changed from a human being into a viper? Shouldn't you, if anything, take pity on her instead?" (v. 8-9, p. 60).
In so many cases, we assume the other person should know better? Have we checked our assumptions? And after having checked our assumptions and learning that the other person needs some educating, are we willing to help them by educating them - by showing them a better way?
The chapter pivots to point out that The Iliad and The Odyssey would not have happened had it not been for impressions and reactions of Paris and Menelaus. The person Epictetus is having a dialogue with acknowledges that wars, the loss of men and razing of cities is simply due to some bad impressions by a few people.
And then Epictetus simply states that wars, razed cities and dead men are no different than dead sheep and birds nests being burned. Now this is shocking to the other person and it may even be shocking to you and me to hear Epictetus so flippantly disregard life and property. But he is willing to teach us.
There is no difference between a man's home and a stork's nest ... both are simply shelters; nothing more and nothing less.
But there is a difference between the man and the stork. He says, "So where in human beings is the great good and evil to be found? In that which distinguishes them as human; and if that is preserved and kept well fortified, and if one's self-respect, and fidelity, and intelligence are kept unimpaired, then the human being himself is safeguarded; but if any of these are destroyed or taken by storm, then he himself is destroyed" (v. 20-21, p. 61).
What makes humans unique, also defines our nature. Our honor, trustworthiness, intelligence - our virtue is what makes us different from the beasts. Living a life according to Virtue is our true nature.
He expounds, using The Iliad as an example: "[It] consists of nothing more than impressions and the use of impressions. An impression prompted Paris to carry off the wife of Menelaus, and an impression prompted Helen to go with him" (v. 12, p. 61).
I apologize for all the copying of quotes, but one more. This is the rub: do we allow our life to be ruled by reactions to impressions? Or do we put thought into our reactions? This is how Epictetus closes the chapter:
"Am I any better than Agamemnon and Achilles, to be satisfied by impressions alone, when they caused and suffered such evils by following their impressions? What tragedy has had any other origin than this? What is the Atreus of Euripides? All a matter of impressions. The Oedipus of Sophocles? Impressions. The Phoenix? Impressions. The Hippolytus? Impressions. What do you call those who follow every impression that strikes them? Madmen! What about us, then; do we act any differently?" (v. 31-33, p. 62).