Epictetus: Destiny, Logos and Happiness
According to the stoic conception, the human being is capable, not only of recognizing the divine world order through reason, but also aligning their acts to it. For stoics, it is good to live in conformity with destiny or nature, through which the world order can be seen. Therefore the wise man must learn to control his emotions in a detached way, in order to face the irreversibility of his destiny like illness and death. This approach and its term of stoic calm has been used until today as a relevant moral ideal through many Western ethical theories and studies.
There are things in our power and others which we can not control. In our power are things like opinions, instincts and aversion, simply put: everything which is our own work. On the contrary, there are things beyond our power like our body, possesions, prestige and social position, shortly: everything which is not our own work. What in our authority resides, can be prevented by nature. Contrarily, what in our authority doesn't reside, is unfree, alien and hindered.
Keep these words in mind: When you take alien and unfree things by nature as free and familiar things, you will suffer from grief, restrain and anxiety. And because of that, you will be unhappy with God and other people. But if you see your own work as your creation, and alien things as something strange and unnatural, nobody will never stop and force you to do things. You won't be unhappy with anybody, work against your will, damage yourself nor have an enemy. You will see how nothing will cause harm to you.