Joseph Campbell described it in his book The Hero with a Thousand Faces.
A hero ventures forth from the world of common day into a region of supernatural wonder: fabulous forces are there encountered and a decisive victory is won: the hero comes back from this mysterious adventure with the power to bestow boons on his fellow man.If you don't take the "region of supernatural wonder" too literally, Campbell's work can be adapted to any genre. Screenwriter and author Christopher Vogler took The Hero with a Thousand Faces to the movies and wrote The Writers Journey: Mythic Structure for Writers. He turned the academic work into a practical guide for storytelling in three acts.
True Grit, Rooster Cogburn's normal is drunk and alone. As a bounty hunter, his call to adventure isn't chasing down a killer, it's chasing down a killer with the victim's daughter. At first he refuses the job, but Mattie Ross convinces him and becomes his mentor for redemption. He then finds an ally in a Texas Ranger, faces ordeals and grouchily takes an inward journey. After being brought to the brink of defeat, Cogburn prevails and returns to his normal world with his bounty.
Something shakes the hero out of their normal state. Things go from bad to worse before the heroes step up and save the day. And they all live happily ever after... at least for now.
*Under A Texas Star