Blake Synder wrote a screenwriting tutorial called “Save the Cat!” The basic idea is that every story needs to create a sympathetic hero, so one method for making your hero sympathetic is to have your hero do something noble like save a cat.
In “Alien,” Sigourney Weaver is trying to get off the doomed spaceship and into the escape pod. Inexplicably, she takes time to grab the cat and put it in a carrying container. By taking time to save the cat, Sigourney Weaver’s character shows that she’s thinking of others. By thinking of others, even if it’s just a cat, you can make a story’s hero more appealing.
Watch any good movie and you can spot this “Save the Cat!” moment when the hero acts selflessly to save someone else. When you see that in a movie, you can tell your friends how you learned this from the “Save the Cat” book.