Stories need causality

A story should flow naturally and gradually unfold.

The way to achieve that is causality. Here is a test to determine whether your film has causality.

When you talk about your story, do you use words like "because of that", "therefore" and "but", or do you use "and" a lot? If it's the latter, it lacks causality.

Most stories, especially good ones, use a structure that goes something like this: "Everyday... until one day... Because of that... Therefore.... Because of that... But.... Because of that...".

Everyday, Luke helps his father on the moisture farms of Tatooine, until one day, they buy new droids and he receives a call for help by the beautiful princess Leia Organa. Because of that, he visits Obi Wan Kenobi. But he doesn't want to leave his family alone. But the stormtroopers kill his family. Therefore, he leaves for Mos Eisley to find a ship.

You get the gist of it.

At the same time, Stories should be unpredictable