One thing that's worth noting is that Epictetus himself was a slave, and I think it's informed a lot of his thoughts. For him, true freedom is being able to overcome the events of the world. You may not be able to control whether or not you're a slave, but (to Epictetus) you can control how you feel about being a slave, and that is true freedom.

ie, he saw the world as full of misery and difficulty, and saw modifying your internal experience as the only possible path forward.