According to Epictetus, Zeus sent us here to earth with the commandment: "Protect what belongs to you at all costs; don't desire what belongs to another."
What truly, wholly belongs to us? It is our perception - our opinion - our attitude.
Indeed, we can prioritize everything in our life, but whatever we decide to focus on, we ought not to resent it (see verse 17).
Epictetus also correctly points out that what we try to protect and cherish becomes a means for us to be enslaved. He says, "If I cherish my body, I make a slave of myself, if I cherish my property, I make a slave of myself" (see verse 23). When we place importance on things that don't belong to us or are not in our control, we only torment ourselves. "In general, remember that it is we who torment, we who make difficulties for ourselves - that is, our opinions do" (see verse 28).
So what should we do? We should practice "maintaining always the same even temper," for this is what Socrates did.
This is why the discipline of assent is so important. We may experience a gut reaction to some event. We ought to pause and in that pause, reflect on whether whatever it is that is trying to bother us. Is it in our control? Does it have sway or power over us? Most likely it does not. And instead, it is our perception that is holding us enslaved. Therefore, we ought to check our assumptions and change our opinion as needed. This is true freedom.