Constantly test your mental impressions - each one individually, if you can: investigate the cause, identify the emotion, apply the analysis of logic.
Whenever you meet someone, ask yourself first this immediate question: 'What beliefs does this person hold about the good and bad in life?' Because if he believes this or that about pleasure and pain and their constituents, about fame and obscurity, death and life, then I shall not find it surprising or strange if he acts in this or that way, and I shall remember that he has no choice but to act as he does.
It would be absurd to be surprised at a fig-tree bearing figs. Remember that there is as little cause for surprise if the world brings forth fruits such as these when the crop is there. Equally absurd for a doctor or ship's captain to be surprised at fever in a patient or a head-wind springing up.
These three passages largely deal with the discipline of assent. The discipline of assent - your inner citadel where you make decisions about impressions - should be an on-going, everlasting dialogue with yourself. It should be the better half of yourself that knows better and knows the right path and the other half of yourself that aligns with who you are on the outside.
The process follows thusly: an external event occurs (a loud banging sound, your boss yelling at you, the moment you realize you've been bitten by a venomous snake, the moment you learn your child has been in a car accident, a death of a loved one). Then comes a gap between your mind processing the external event and the real you arriving at a decision to be impressed or not. It is in that split second of a gap where the discipline of assent aims to fix and widen. If you have an on-going dialogue in your mind, you are able to extend that gap slightly and allow yourself time to process the external event before reacting. One of the practices that Stoics teach is to simply break everything down so as to break impressions that have already formed. Are you naturally inclined to be impressed by delicious food? Then break the food down into components. It is not sizzling, crackling, steak that is so sumptuous to the taste; rather, it is a dead animal, that has been slaughtered, guts split, blood emptied, sliced into chunks of flesh, and cooked over a skillet. In short, it is a piece of dead animal. If successful, you have broken the allure of steak and now you can choose whether it is good to find contentment in eating that dead animal or not. The more one practices this "breaking of things down" the wider the gap is between external event and impression. Hopefully, you can logically choose your impression rather than automatically choosing based on your animal instincts.
Included in the category of externals are people. You do not have control over other people, therefore they are in the domain of externals. And when you deal with other people, it helps to analyze them to understand where they place their contentment. Do they seek contentment in externals (do they seek pleasure and avoid pain? Do they seek fame and are worried about being obscure? Do they fear death?) If so, then it should not surprise you when they act badly.
Lastly, don't be surprised by kids acting like kids and unphilosophical people acting unphilosophically.