If you’re interested in writing a screenplay, you can read Blake Snyder’s book “Save the Cat!” The phrase “save the cat” comes form the author’s belief that in order to make your hero likable to your audience, you hero has to do something noble such as save a cat. That immediately makes the audience want your hero to succeed.
Even in a movie like “Alien,” Sigourney Weaver took time out to save the cat. When the hero takes action to save someone else, often at great sacrifice to him or herself, that makes the hero’s quest to achieve a goal all the more important. If an audience doesn’t like a hero, they won’t care if that hero achieves that goal or not. If the hero likes and even loves the hero, then the hero can pursue the simplest goal and the audience will still cheer the hero on.
And to think it all comes from trying to save a cat.