Callisto's name means "most beautiful," and that's definitely not false advertising. This nymph is one of prettiest of all of Artemis's flock. Of course, her beauty definitely doesn't turn out to be a particularly good thing for her, since it's her good looks that perk the interest of Zeus. After the dirty old god seduces and impregnates her in the form of her beloved goddess, we're guessing Callisto might've wished her name meant "kind of plain."
Unlike a lot of figures in Greek mythology, Callisto doesn't do anything—seriously, nothing—to deserve all of the bad stuff that happens to her. Sure, she sleeps with Zeus, breaking her vow of chastity, but she thinks she's being seduced by the very goddess to whom she swore the vow. Shouldn't that cancel it out or something?
What do you think, then? Is it unfair when Artemis turns Callisto into a bear as punishment?
In the end, Callisto finally catches a break—kind of. When her son, Arcas, is about to shoot her, thinking she's a wild bear (which she is, we guess), Zeus steps in and transforms them into the constellations Ursa Major and Ursa Minor. So even though Callisto really gets a bum deal in this story, at least she's spared a totally tragic ending. Being a constellation is a big honor, after all.