The Hero's Journey is a framework that scholar Joseph Campbell came up with that many myths and stories follow. Many storytellers and story-readers find it a useful way to look at tale. (That's actually putting it lightly. Some people are straight-up obsessed.) Chris Vogler adapted Campbell's 17 stages of a hero's journey, which many screenwriters use while making movies. Vogler condensed Campbell's 17 stages down to 12, which is what we're using. Check out a general explanation of the 12 stages.
The story of Callisto doesn't fit perfectly into the Hero's Journey structure, but we're giving it a shot. As the gross old saying goes, there's more than one way to skin a cat.
Callisto is living a good and chaste life as a virginal follower of Artemis. The beautiful nymph is totally content and everything is cool.
When Zeus seduces Callisto in the form of Artemis, the nymph is tricked into breaking her vow of chastity.
In some versions, Callisto tries to fight off Zeus when she figures out what's going on, but the king of the gods is too powerful for the nymph.
You could see Zeus as a mentor figure in a kind of a gross way. After all, he is the guy who gets Callisto started on the painful road she's about to walk down. Callisto's real mentor, however, is Artemis, whom she loves and respects.
When Artemis discovers that Callisto is pregnant, the nymph's old mentor punishes her by transforming her into a bear. Callisto has now been given the boot from her old life.
It seems like Callisto doesn't really have any friends at all. Everybody's either seducing her under false pretenses or punishing her for stuff that's not really her fault. After some hunters take her son Arcas away, the poor nymph-turned-she-bear has no one around at all.
Callisto doesn't even know that she's approaching the inmost cave when it's going down. She's just been wondering around the woods being a bear for years, when one day she unknowingly wanders near her son, Arcas, who's out for a hunt.
Zeus steps in before Callisto's ordeal can go down. Instead of letting her be killed by their unwitting son, the god transforms them both into constellations.
We guess being turned into a constellation is kind of a reward. However, we have a feeling Callisto would've preferred to stay a beautiful nymph forever and never have been turned into anything at all.
Sorry, myth's over! No road back for Callisto.
We told you, it's done.
Seriously, that's it.