Source, Epictetus, Enchiridion, 1
Some things are within our power, while others are not. Within our power are opinion, motivation, desire, aversion, and, in a word, whatever is of our own doing; not within our power are our body, our property, reputation, office, and, in a word, whatever is not of our own doing. The things within our power are by nature free, unhindered, and unimpeded; the things not within our power are weak, servile, subject to hindrance, and not our own.