The Enchiridion, Section 2 — In Plain English

Epictetus — The Slave

Remember what desire and aversion really mean. When you want something, you're demanding to get it. When you hate something, you're demanding to avoid it. If you don't get what you want, you're disappointed. If you run into what you hate, you're miserable. So here's the key: only avoid things you can actually control. Then you'll never hit something you're trying to avoid. But if you try to avoid sickness, death, or poverty, you're setting yourself up for misery. Stop being averse to things outside your power. Save that energy for bad things you can actually control. For now, put all desires on hold. If you want things outside your control, you're guaranteed disappointment. And you're not even good yet at wanting the right things — the things you can control. When you absolutely must go after something or avoid something, do it carefully, gently, and in moderation.

Epictetus — The Slave Original

Remember that desire demands the attainment of that of which you are desirous; and aversion demands the avoidance of that to which you are averse; that he who fails of the object of his desires is disappointed; and he who incurs the object of his aversion is wretched. If, then, you shun only those undesirable things which you can control, you will never incur anything which you shun; but if you shun sickness, or death, or poverty, you will run the risk of wretchedness. Remove [the habit of] aversion, then, from all things that are not within our power, and apply it to things undesirable which are within our power. But for the present, altogether restrain desire; for if you desire any of the things not within our own power, you must necessarily be disappointed; and you are not yet secure of those which are within our power, and so are legitimate objects of desire. Where it is practically necessary for you to pursue or avoid anything, do even this with discretion and gentleness and moderation.