All film making, and all storytelling, has one primary objective: to elicit emotion in the audience. This objective is achieved with only three basic elements, which form the foundation of all story: character, desire and conflict.

The basis of all good myths, legends, epic poems, fairy tales, plays, operas, short stories, true stories, novels, screenplays, TV episodes, movies and Harry Chapin songs is simply this: emotionally involving characters must overcome seemingly insurmountable obstacles in order to achieve their compelling desires. This single sentence must therefore form the foundation of any screenplay your hope to sell to Hollywood.

Because screenplays and movies are so much more narrowly defined than any of those other forms of fiction, anyone adapting an existing story into film must abide by strict rules of character, desire and conflict. In a movie, the character must be a hero or protagonist with whom we empathize, who is pursuing a visible goal with a clearly defined end point, and who must face terrifying obstacles created by other characters or forces of nature.

This visible goal - what I term outer motivation in my book and seminars - must have a clearly defined end point or finish line. It defines the story concept or log line of the film, it will give the audience a clear idea of exactly what they're rooting for the hero(es) to achieve, and it tells us exactly what will represent success for the hero at the end of the film.

This is the challenge if you're writing an adaptation: no other story form has these same requirements. Novels, plays and true stories, for example, can follow multiple characters through long expanses of time as they pursue a series of desires. Their goals can be interior - a desire for acceptance, for example, or to resolve some inner pain just by living through it. And in biographies, the protagonist may go through many highs and lows of achievement and failure as we follow her life from beginning to end.

But successful Hollywood movies follow a stricter formula (and if you consider formula a dirty word, screenwriting may not be your most fulfilling path as a writer). Movie heroes also pursue acceptance, or revenge, and may also want to resolve relationships or inner conflicts. But if these goals don't grow out of clearly defined outer motivations, the movies simply won't get produced, or won't successfully reach a mass audience.

In Titanic, Rose longs for passion and adventure; in Shrek, the hero would love to be accepted and find true love; and the heroes of Star Wars, Working Girl and Stand By Me all need to accept themselves and stand up for who they truly are. But all of these invisible inner motivations would be static and uninvolving if these protagonists' visible goals were not to get to America with Jack, capture the princess to get his land back, or stop the Empire, set up the takeover, or find the dead body.

Movies can even tell life stories, but if the subject's life is not defined by a singular visible desire -- winning Jenny's love in Forest Gump, for example - the film will likely be a disappointment at the box office.
So where does all this leave you if you want to write an adaptation?

The most successful adaptations originate as stories that already have clearly defined story concepts.

At the time I'm writing this, the top ten adaptations of all time at the box office (not including sequels) are: Jurassic Park; Forrest Gump; Harry Potter and the Sorcerer's Stone; Shrek; How the Grinch Stole Christmas; Jaws; Batman; Lord of the Rings; Mrs. Doubtfire; and The Exorcist. In every single one of these stories, the hero's visible goal is clearly defined, the log line is easy to express, and we know immediately exactly what represents success for the hero: stopping the dinosaurs; winning Jenny's love; capturing the Sorcerer's Stone; retrieving (and winning the love of) the princess; stopping Christmas in Whoville; stopping the shark; stopping the Joker; getting the ring to the volcano; getting to be with his kids; and exorcising the devil from the girl.

If you're tackling a novel that follows a long expanse of time and multiple heroes, see if you can extract the central character and a single goal from all that you have to choose from. The more focused and finite your story concept, the more commercial your screenplay will be.

Avoid biographies that follow heroes through a series of big events or desires.
Life stories may be compelling on A&E, but as films they almost always fail at the box office, or struggle to break even. Chaplin, The Babe, Cobb and Hoffa may be about unique, larger than life figures, but the movies give us nothing specific to root for, and lost a ton of money.

There are two ways to overcome this dilemma: select subjects whose lives are devoted to a single, visible outcome (freedom for India in Gandhi; freedom for Scotland in Braveheart); or pick a single incident from the life of your subject and make that the outer motivation of your movie. The written biography of John Nash reveals an abundance of events and conflicts throughout his life, but the movie focuses specifically on his and his wife's battle against schizophrenia within a much shorter period of time. And Erin Brockovich is the story of a woman who wants to win a lawsuit against PG&E - none of the rest of her life is included.

Your allegiance must be to the movie, not the source material.
Because the goal of all story is to elicit emotion, it's easy to assume that because reading something is captivating, the screenplay of it will be as well. But novels and plays and newspaper articles operate under different rules and parameters. Florid passages of prose, deep, meaningful thoughts or long monologues that sound good on the stage must be eliminated from your screenplay.

Pleasing the author or the people that loved the original novel is also not your concern. Your job is to get a Hollywood executive excited about your movie, even if it means changing, or omitting altogether, your favorite parts of the book.
It's because of this principle that you should probably…

Avoid adapting your own books and plays.
I know this comes as harsh advice for many of you, since it's probably the main reason you bought this book in the first place. But it is next to impossible to maintain the ruthless objectivity necessary to change the treasured moments of your original work in order to maintain proper movie structure. And if your manuscript sits unpublished, or your play unproduced, in its original form, it's unlikely it will succeed in the much more competitive world of Hollywood.

Of course, all this changes if someone's offering you money for the film rights to your work. Once your novel or play has proven itself in its original arena, you can attach yourself as screenwriter and hope that its prior success peaks Hollywood's interest.

Of course there are exceptions to these rules. The Shawshank Redemption; The Green Mile; The Shipping News; Driving Miss Daisy; Terms of Endearment; A River Runs Through It; Ordinary People - none of these films has a visible outer motivation for the hero, many cover long expanses of time, and yet they were all very successful at the box office. But they were also based on very successful books or plays, were written by well established writers or writer/directors, and/or were driven by the stars or directors who were passionate about them. And they form a tiny percentage of the films coming out of Hollywood.
So if you're a new writer hoping to launch your career, I'd concentrate on adaptations that give you your greatest chance of success: stories that already contain the elements that have proven to be the foundation of Hollywood's most successful movies.

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Michael Hauge, author of Writing Screenplays That Sell, is a screenwriting coach and teacher who consults with Hollywood writers, directors and production companies. For information on his seminar schedule or his consultation service, please call 1-800-477-1947 or visit his web site at ScreenplayMastery.com.