In mythology, Cassiopeia was the vain wife of Cepheus and mother of Andromeda. If she had not boasted that her beauty was greater than that of the gods, then she would not have brought so much suffering to her family! Milton described her as the braggart queen bringing destruction down on the heads of her household by saying that her beauty and that of her daughter was greater than the sea nymphs of Poseidon. He then sent Cetus, the sea monster to ravage the land until Perseus destroyed it and saved Andromeda.
If she had not done so, we would then have a sky full of constellations with different names now, as Cassiopeia is an inseparable part of the Perseus legend.