“Every event has two handles—one by which it can be carried, and one by which it can’t. If your brother does you wrong, don’t grab it by his wronging, because this is the handle incapable of lifting it. Instead, use the other—that he is your brother, that you were raised together, and then you will have hold of the handle that carries.” - Epictetus
For every challenge, we must train our minds to see the different ways of handling a situation. Epictetus is trying to teach us here, or be made aware of, that if you focus on the negative handle, you will get a negative result. But, on the other hand, if you commit to finding the positive in a situation by acting with temperance, wisdom, courage, compassion, and love, then you are more likely to be in a mindset that will enable you to find the best solution possible.
If you are trying to quit smoking, for example, you might have this voice in your head: "Just one last one, I really want to smoke. It's so hard to quit, to give up the habit. I miss it." Or you can have another voice that says: "I didn't quit smoking; I started breathing properly again. Now I can run with my kid for more than 5 seconds without spitting out charcoal."
You get to choose what voice you focus on. It doesn't matter if you hear both. You have the freedom to listen to just one.
To finish off, I think it's important to mention that Epictetus is not telling us always to be super positive and act like blind optimists. Instead, he is telling you that there are different perceptions of a single situation and that you have control over your interpretations of events. Else, that makes you a victim of life. So control your perceptions and direct your actions willingly.