This is the monomyth:
There is a hero with whom the audience feels a sense of connection or kindredness. The hero is not the most powerful version of their that they could be, but a sense of the status quo has kept them from the arduous task of mastering their self and pursuing their fate.
Then something bad happens. Someone dies, or there is some threat on their self or someone they love—it can be anything, so long as it motivates the character to leave their comfort zone. For Bilbo in The Hobbit, it was the money on the other side of slaying the dragon. For romance novels, it's often the damsel in distress.
After the person leaves their home, they enter into a journey with various quests and challenges. There is often a helper who reminds them of their power (like Yoda in Star Wars), and many times there is also a love interest who spurs the hero on in difficult times.
The hero is called upon to sacrifice parts of their life that they don't want to let go of, because they need to shed the weight and persist with a more singular sense of purpose.
Finally, after a long journey, the rising action comes to a head, and the hero has to face the dragon, or the darkness, or whatever it was that they couldn't succeed against originally. In an act of bravery, the hero uses his training and intuition to defeat the enemy before returning home.
But when he gets home, he is not the same man. He is the best version of himself he can be for his journey, and he is the king of his domain.
This monomyth is what Campbell argued was the story of all human myths and stories.
