The Stoic world is different to ours, so let's break it down, one big idea after another.
1. Man's Nature
Whether it was Nature, Fortune, Evolution, or God, the fact of the matter is that we are distinguished from other living beings by two things: our reason and our social nature.
Our reason allows us not only to problem-solve & communicate, which is an ability that many other creatures posses, but also to ponder our own thinking, which is a feature that, as far as we know, does not exist anywhere else in the world. This idea seems obvious, but we put little effort in embodying it, often behaving like beasts by yielding to impulses, passions and unexamined desires. Imagine a cat that doesn't know how to hunt, a dog that doesn't know how to bark, or a bee that cannot find a flower; this is man without his ruling faculty, a being that has lost itself.
The Stoics remind us that, aside from our reason, we are also distinguished by our socialness. Unlike spiders, snakes & cats, human existence relies largely on the contribution of other members of its own species. This has been the case since we started forming tribes and has become even more of a phenomenon in the modern world, where every product or service we touch is brought to us by humans, sometimes many hundreds miles away. And more than this - we share a common bond, the experience of being human, of having our special form of reason, that we do not share with anything else in the same way. In this we are tied through our nature. So when we are met with other humans, we say: "Here is another person who has been blessed with the faculty of choice. He is my brother. She is my sister. No matter what external factor separates us, this we both share."
2. The Dichotomy Of Control
Some additional context before we dive into this topic.
2a - Ownership
The Stoics had a very strict definition of ownership. For the Stoics, you owned only what could never be taken from you. Under this strict definition, only your thoughts and choices are yours. No amount of torture, for example, could convince you that the sky is actually purple, if you do not assent to this idea yourself, even if you say the words out loud. No one can force you to believe something that you don't believe, unless you have assented to this belief. It follows then, that all things outside of choice, including money, fame, health, reputation, property, friendship, love, are not truly ours because they are not within our control. Your money can be taken from you by your employer. Your wife can be taken from you by death or another person. Your child as well. Your reputation is in the hands of others. You can prepare for years and then in your defining moment as a tennis player, you can slip on a piece of paper and lose the trophy you've been chasing all your life. A judge could rule 'guilty' and take your freedom. All these things that are lauded as 'yours' can be taken from you. So what remains that is truly our own? Only our choice, the Stoics say.
2b - The World Order
Orthodox Stoics like Epictetus believed that the world is governed by a benevolent, ordered, logical creator. They believed everything was made to fulfil a purpose, and they used the forms and functions of things to understand what that purpose was. A bee, due to its wings and its natural habit of going to flowers and creating honey, was made to fly and make honey. That is its God-ordained purpose. Similarly, human beings, with their reason and social nature, were designed to live reasonably and socially with one another.
Now, let's return to this idea of ownership. Ownership is a simple but powerful because it leads us to unconventional places. Take this example. To the normal person, death is a horrific thing to be avoided, but to the Stoic, death is just one other thing that is not within our control, so we must learn to accept it. Now replace 'death' with literally anything that is not 'choice,' and the idea leads you to the conclusion that nothing can be good or bad that is not within your choice, only indifferent.
Again, you are in a bizarre place - your wife is not good, she's an indifferent, because she can be taken from you. Your children are not good, they're an indifferent, because they can be taken from you. Your health, wealth, etc.. everything the world tells us is good, the Stoics tell us is an indifferent. It is your inaccurate judgement that makes you say what is indifferent is either good or bad.
Let's push the idea even more. If nothing outside of our sphere of choice is good or bad, then where do good and bad come from? The Stoics say they come from our choice - from how we decide to react to external events. Let's take the example of losing your leg. The Stoic would say: "Since your leg can be taken from you, it's neither a good nor a bad but an indifferent. Also, since the world is governed by an all-knowing, benevolent creator, then losing your leg is just part of the broader story of God. Therefore, since reason dictates that losing your leg is neither good nor bad, and since losing your leg was ordained by an all-knowing, benevolent creator, then to live according to our purpose would be to bear this indifferent well. To bear it well, we should avoid becoming angry and sorrowful, and instead aim to tame these emotions and maintain our happiness for properly fulfilling our role in the broader story. Basically, the Stoics say you're supposed to think of yourself as an actor in a play; You do not decide what happens to your character, so you must just read the lines and play the part as well as you can. The director is also the GOAT, so you don't want to question or disappoint him, so do your part well & without moaning!
3. Practicing Virtue
With this context, we can now discuss how the Stoics arrived to the idea that by consciously examining one's impressions of the external world and arriving to the right response, one can live a virtuous life, encompassing both one's rational and social nature as a member of the broader cosmic whole.
The Stoics basically say that the world is just a series of stimuli. You receive praise from a stranger. This is a stimulus. Your leg is broken. This is a stimulus. Your neighbor's wife looks at you sexually. This is a stimulus. You see a grand mansion. This is a stimulus. Humans often jump from stimulus to judgement without recognizing the leap. You receive praise from a stranger, you acknowledge this as good, and you smile. Your leg is broken, you acknowledge this as bad, and you cry. Your neighbor's wife looks at you sexually, you acknowledge this as good, and you have sex with her.
The Stoics tell us that we are constantly making miscalculated judgements about what is good and what is bad without conscious awareness. A virtuous person, according to the stoic, pauses to reflect on these judgements, considers it, weighs whether it's a good or a bad, and then takes the choice that reflects the 'true' good. So to do right, you must know two things: the nature of good and bad (which we have discussed), and how to spot and calibrate miscalculated judgements. The first part is easy; the second is what most are never able to sustain and what makes Stoicism a life-long practice.
Consider the example of the neighbor's wife. Your lust tells you that pleasure is good. But we have examined the nature of things and come to the opposite conclusion - that pleasure cannot be good because it does not come from choice. Moreover, sleeping with your neighbor's wife is a breach against our social nature because it harms the neighbor's husband and betrays trust between humans. The impression, therefore, that your neighbor's wife coveting you is a desirable thing, is in fact incorrect. The correct action would be to ignore her advance. The even more correct action would be to change your view that your neighbor coveting you is something worth smiling about.
Under the Stoic lens, life is just a series of these mini-stimuli. The philosopher has acknowledge the true nature of good and bad. More importantly, he has trained himself against the strong desires that leads one to believe that good and bad exist outside the realm of choice. These are some of our strongest desires - embodied via the pursuit of pleasure and the aversion to pain. The Stoics demand you command these to live a virtuous life.
Through these three key points, the Stoics provide an instruction manual on how to deal with the world so that you come out of it happy. While I do not agree with everything in here, some of the stuff is just too good to ignore.