Discourses, "On Anxiety Solicitude" (§3)

“For this reason, when Zeno was going to meet Antigonus, he was not anxious, for Antigonus had no power over any of the things which Zeno admired; and Zeno did not care for those things over which Antigonus had power. But Antigonus was anxious when he was going to meet Zeno, for he wished to please Zeno; but this was a thing external (out of his power). But Zeno did not want to please Antigonus; for no man who is skilled in any art wishes to please one who has no such skill.”