The Judgment of Paris is the very famous Greek myth, so famous that I will give a brief summary of it. (With Ruben's famous picture.)
At the wedding of Peleus and Thetis all of the Greek gods and goddesses were invited except Eris, the goddess of Discord. In a fit of rage, she arrived and threw one golden apple in the air, saying, "Let the fairest claim it." Three goddesses claimed it: Hera- the queen of the Gods and Zeus's wife, Athena- the goddess of Wisdom, and Aphrodite- the goddess of Love. The king of the Gods, Zeus, would not settle the dispute over who was the fairest because he would have been in hot water if he'd chosen anyone but Hera. Instead he passed the duty off to a sheepherder named Paris.
Paris was actually the child of Priam, the king of Troy, but he had been abandoned on a mountain because it was foretold that he would bring the destruction of Troy. As a sheepherder though, the three goddesses asked him to choose the most fair among them. Hera offered him power and riches; Athena offered him wisdom and glory in battle, and Aphrodite offered him the love of the most beautiful woman in the world. Paris chose Aphrodite and earned the hatred of Athena and Hera forever.
His choice also doomed his kingdom, his city, his friends, and his family because the most beautiful woman in the world, Helen, was already married to a Grecian king. Once Paris stole Helen from Greece and took her to Troy, the Greeks declared war on Troy. It lasted 10 years, and when the Greeks finally won (via Trojan Horse) every warrior or ally of Troy in the city was slaughtered.

What a happy story! You can probably pick out two important themes from that story that were-

1) Choosing love over everything else. Paris ignored all the dangers and costs of his decision and went for love. It killed everyone, and no one was ever happy, but he had love. He valued love more than wisdom, power, glory, or riches, and he sacrificed all he had to keep it.

2) Making a choice that is so irrevocable you can never take it back and change things. There were three equally attractive choices, and once one was made, nothing would ever be the same.