On the opinion laid over the thing
“Men are disturbed not by things, but by the views which they take of them.”
Between an event and our distress there is always a sentence — usually silent, usually unexamined. The delayed train is not the problem; the problem is “this ruins everything.”
Epictetus is not asking you to pretend the train is on time. He is pointing at the narrow gap where the opinion gets added, and suggesting that the gap is yours. Most of what we call reacting is really agreeing with something we never said out loud.