Phaethon, in case you aren't familiar with the story, is a human son of the Sun god in Greek legend. He travels to his father's palace to confirm his parentage, and to prove that he is in fact his father, the Sun god offers Phaethon any boon he asks. Phaethon asks to drive the chariot of the sun across the sky for one day.
The Sun god reluctantly agrees, because he knows how difficult and treacherous the path is. He warns Phaethon, who doesn't listen, and the chariot takes off. After a short time the kid is disoriented and terrified, and loses control of the horses. The chariot leaves its ordinary path across the sky, and flies too high, scorching the skies. Then it swerves too close to the earth and burns whole sections of the earth. Zeus, looking down to see why the earth is smoking, sees Phaethon and sends a lightning bolt to shoot him out of the sky. Phaethon crashes to his death, and Zeus floods the whole world to put out the fire.
It could be said that Phaethon and Icarus are bookend stories; afterall, each flies too high and is brought down. But Icarus delights in his flight. His is a triumph, until the very end. Phaethon is different: his motives are to prove himself. Even in the beginning of his flight, he is terrified. Then he loses control and the nightmare begins in earnest. There is no sweet moment of triumph, no victory. There is only fear and terror, insecurity and inadequacy.