I had occasion today to mention the "sword of Damocles" in conversation, but then realized I didn't really know what exactly I was talking about. Wikipedia provided the explanation:
According to the story, Damocles was pandering to Dionysius, his king, and exclaimed to him that Dionysius was truly fortunate as a great man of power and authority, surrounded by magnificence. In response, Dionysius offered to switch places with Damocles for one day so that Damocles could taste that very fortune firsthand. Damocles quickly and eagerly accepted the king's proposal. Damocles sat down in the king's throne surrounded by every luxury, but Dionysius, who had made many enemies during his reign, arranged that a huge sword should hang above the throne, held at the pommel only by a single hair of a horse's tail to evoke the sense of what it is like to be king: though having much fortune, always having to watch in fear and anxiety against dangers that might try to overtake him. Damocles finally begged the king that he be allowed to depart because he no longer wanted to be so fortunate, realizing that with great fortune and power comes also great danger.
King Dionysius effectively conveyed the sense of constant fear in which a person with great power may live.