Why write more back story than what will end up in the movie?

Would a few sentences be enough for you to pretend to be a different person? Would a few sentences be enough for you to understand the person’s history, way of thinking, emotions, actions, etc, well enough to portray them?

The way a person acts and reacts to situations is defined by that person’s history. The way YOU react to any given situation is defined by your own personal history, what you have experienced over your life time. If you gave a stranger a 2-sentence summary of your character, do you think that would be enough for them to accurately portray you, how you would react in any new situation?

Personally, I don’t.

The way that the actors give depth to the characters is by having back story. It helps them get into character and react the way their characters would react to various situations in the script.

As a writer of short stories and a lover of movies and the theatre, I can assure it’s important, if not essential, for a writing a back story for each of the characters. It gives the him a clearer idea of the characters’s identity, personality and motivations, relationship to other characters—and where to take them in the plot. That in turn gives the actor more grist for developing his or her character. Even when the writer doesn’t provide this information in writing, a dedicated actor will develop his own back story.

I can’t even play a D&D character without writing the character’s life story out. How else would I know how the character would react to every situation?

I’ve been developing the back story to my “world” on and off for somewhere between 12 and 14 years, and I don’t even have a publishable story on paper yet. I have hundreds of anecdotes and a fairly elaborate plot, but I don’t feel like I know my characters well enough yet to dictate their actions.

Think of it this way – Tolkien is still releasing new material, and he’s been dead for almost 40 years.

With many films, the path the narrative is going to turn out is unknowable until almost the final stages before release. There are shooting scripts and storyboards, but the final product is always in flux and is rarely a carbon copy of the original screenplay.

Likewise, a writer doesn’t know the end of a story until they have written it. Rather, they discover it as they write.

Writing backstory is an exercise in discovery. The story that is later written out of that exercise will have a more cohesive plot and more believable and developed characters, than a story written “on the fly.”

The backstory can sometimes be published as a prequel, if the author chooses to do so.

The back story is primarily for two things, the writer’s subconscious and to allow the story and opportunity to contribute to the creation of the character. What I mean by the latter is true art is a collaboration of the artist and the medium. The deeper the back story, the more chance you give your story (the medium) to shape its own world and subsequent possible choices and resources available to your character that would be otherwise unbeknown to the writer just from the plot. Secondly I say it is for the writers sub conscious because you would be amazed at how quickly an audience will pick up in the blank spots of your stories background that they do not need to know, but definitely feel something missing. Like for example when the interaction of two characters seemed forced or contrived. The reason for this is because the characters interaction, without a back story (clear in the writers subconscious) exists only to drive the plot and that feels contrived. With the back story clear the dynamics become based on how these two have always treated each other and why; the secrets they have kept or the girl the both dated. That sits in the writers subconscious and makes the characters more real, with inside jokes or sarcasm that they would not have possibly had beyond that plot moment. The same I would imagine could exist for the actor, however I believe if the writer truly did their job, the subtext might be enough for the actor to really get into the head of the character after a few reads of the script.