At the center of Epictetus' teaching is the acquisition of happiness. A necessary condition is to know which things depend on us and which do not. Those that do not depend on us, we must know that we cannot change them and we must simply tolerate them, as it is futile to worry or fight against them. We can only change those things that depend on us and thus we can control ourselves in order to achieve happiness.
This distinction that Epictetus makes is particularly important. If we cannot make this distinction, we are condemned to consider important things that are actually insignificant.
For Epictetus, it is important to adapt to what happens in our lives and not to consider them as good or bad, but as indifferent. The indifferent things, therefore, whether they have a positive content (health, life, wealth, friends, family, etc.) or negative (death, illness, poverty, etc.), do not lead to the conquest of happiness, which is characterized by apathy and tranquility.
To face the adversities of life with calmness, without losing our inner peace, we can achieve it by correctly evaluating our perceptions of things.