Because it's also the script to every good story ever.
Hero's journey:
- Thing happens that sends someone on adventure
- Person is flawed, and flounders for a bit
- Person meets mentor, receives magic sword from mentor
- Person is semi-competent with magic sword and better than he was
- Person fights big bad, but it's too early and moral failing prevents him from adequately using magic sword so he loses
- Person collects himself, examines why he lost, grows as a person, and becomes better at swinging magic sword
- Person beats big bad, usually with friends who used to be enemies.