The first part of this chapter and the last part of this chapter are pure gold.
What makes us unique? What defines us?
The Stoics would say that the obstacle is the solution to our problems. Life throws challenges and curve balls at us and how we respond to them reveals who we really are.
Epictetus says, "it is difficulties that reveal what men amount to." When difficult times - challenges or obstacles in our path - come to us, how we react to them reveals who we really are. And we need to be of the mindset that these challenges and obstacles are opportunities for us to prove ourselves - they are gifts for us to "rise to the occasion." We can learn and read our Stoic principles all day long, every week, month after month. But if we never have the occasion to prove that we have embraced them, then what have we accomplished? Give me a challenge and I will show you what I've learned - what I have become - who I am. Gold is revealed in the rock after the fire purges out all the waste. Epictetus reminds us that whenever difficulties come into our lives, "remember that God, like a trainer in the gymnasium, has matched you against a tough young opponent."
Epictetus tells his students how the true character of Diogenes was revealed. Diogenes wore the bare minimum of clothing. He slept on the bare ground. His proof of success was his confidence, his serenity, his freedom and his tough and radiant physique (see verse 8).
Certainly, you can avoid the challenges and obstacles; you can even exit through the door - permanently. But if you do so, you'd be a greater coward than children. Children will flippantly decide to not play anymore when they don't get their way - they disengage from the challenge or obstacle. Is that who you are? Or maybe you're the type who is not willing to exit through the door, but will still complain and carp and constantly be pissed off. That certainly is no great existence either.
The best solution, according to the Stoics, is to face the challenge - embrace it - engage with it. You will fail, and that is fine. But keep moving forward; pick yourself up and get back in the game. More challenges and obstacles will come. So learn from the previous ones and improve when you meet the next round of challenges and obstacles. Allow yourself to be defined by your trials - after all, they are yours.