There are things that are within our power, and things that fall outside our power. Within our power are our own opinions, aims, desires, dislikes — … - Epictetus

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There are things that are within our power, and things that fall outside our power. Within our power are our own opinions, aims, desires, dislikes — in sum, our own thoughts and actions. Outside our power are our physical characteristics, the class into which we were born, our reputation in the eyes of others, and honors and offices that may be bestowed on us.
Working within our sphere of control, we are naturally free, independent, and strong. Beyond that sphere, we are weak, limited, and dependent. If you pin your hopes on things outside your control, taking upon yourself things which rightfully belong to others, you are liable to stumble, fall, suffer, and blame both gods and men. But if you focus your attention only on what is truly your own concern, and leave to others what concerns them, then you will be in charge of your interior life. No one will be able to harm or hinder you. You will blame no one, and have no enemies. If you wish to have peace and contentment, release your attachment to all things outside your control. This is the path of freedom and happiness. If you want not just peace and contentment, but power and wealth too, you may forfeit the former in seeking the latter, and will lose your freedom and happiness along the way.