In my blog over the years, I have written a lot about story structure. Story structure is all about the foundations of a story. From childhood we are introduced to stories and quickly understand their patterns. Once-upon-a-time… and they all lived happily every after.

Remember this one:
Jack takes his family cow to sell, but naively exchanges it for worthless beans. His mother is annoyed and throws the beans away. Up shoots a bean stalk. Jack steals the hen that lays the golden eggs from the giant and escapes down the beanstalk. And chops down the beanstalk before the giant can catch him.
We have all the basics here. A protagonist to identify with — Jack. An opportunity/problem that comes into his life — a quest to recover the hen that lays golden eggs. An antagonist to complicate matters — the giant. A climax — jack escapes from the giant and cuts down the beanstalk. And a character arc — Jack goes from naive child to hero.
As we get older the storylines get a little more complex but we still see the same underlying patterns.
Most romance stories have a simple plot. Boy meets girl. They initially dislike each other but are forced together. Love blossoms. Something goes wrong that forces them apart and then the lovers reconcile.
Most action stories are good-versus-evil stories. The protagonist underdog puts his life on the line to save the world. And just when evil seems triumphant, he/she manages to pull off the impossible and defeat evil.
There are coming-of-age stories when a young protagonist learns to stand up for themselves or overcome some weakness. And there are redemption stories where a flawed protagonist learns the true meaning of life (Christmas Carol).
Mystery, crime and horror all have their own patterns too. And they have their tropes: the down-and-out PI, the studiously clever detective that solves an impossible crime, or the selfish group of kids that provoke the ire of some psychopathic killer.
There is something about stories that we recognise in our emotional DNA and that we never seem to get enough of. We want to root for hero/heroine to win the day, but usually not until they have survived enough pain. Winning should never be effortless.
So as writers we need to understand these patterns are at the very heart of our stories. In any story there are two fundamental storylines. The main plot or protagonist’s outer journey, and the character arc or protagonist’s inner journey. But these two story lines are by no means the only elements we see in a modern novel or movie. Otherwise we would be limited to writing fairy tales.
So novels and movies weave in a number of important storylines about protagonist’s relationships with other main characters: the antagonist, the love interest/buddy, and sometimes a mentor/confidant, or sidekick. These are no less important than the two main storylines, because they add colour and realism to the characters and are the reason we connect with them. Combining all these storylines into one a cohesive story is by no means easy. But writing is a craft that requires both talent and technique and, like most crafts, takes time to develop.