Scripts are the things that movies get made out of.
The Myth: Screenwriter dreams up amazing story while working minimum-wage job at 7-11
The Reality: Producer thinks of story, hires writers to create synopsis and treatment detailing scenes.
The Myth: Screenwriter perfects his script through multiple late-night rewrites, while caring for his dog who has cancer.
The Reality: After plot is worked out, producers hire an established screenwriter (less than 2,000 of who are employed in Hollywood annually)
The Myth: Screenwriter takes script to famous director, who tells screenwriter he's awesome and says that he's sorry about his dog; offers to finance film personally.
The Reality: Hired screenwriter and producer assemble pitch, present to potential financial backers (studios, individuals or government councils).
The Myth: Movie is made by quirky independent studio that can work on a low budget.
The Reality: In recent decades most 'independent' studios have been bought out by larger ones. The average film now costs around $100 million, $35 million of which goes to advertising.
The Myth: Once the movie people like you, it's all hookers and blow, your dog can get lifesaving cancer treatment, and your fame is everlasting.
The Reality: Most movies stall in the development phase and never get made. This is known as 'development hell'.
The Myth: You retain some creative control over the movie, or at least can hand it over to an awesome auteur director, and the two of you hang out and like, trade ideas.
The Reality: Directors are usually hired after the storyboards have been created, the sets constructed, and the already budget worked out, and therefore have little creative control.
The Myth: But at least your director buddy has control after he joins up, right?
The Reality: The producers monitor the movie daily, and can 'suggest' changes if they don't like the director's work. Studios can demand changes on a whim and can even require test screenings, during which bored audiences will probably change your deeply-tragic-but-meaningful ending to a final scene where the character wakes up to realize it was all a dream. They can also get bored and decide your movie will go straight to DVD.
The Myth: At least you can make sure your art isn't tastelessly commercialized!
The Reality: Advertising and merchandise are determined purely by distributors (which are often owned by the studios themselves) not by the people that made the movie.
The Myth: Although the process sucks, at least your product is keeping those mom-and-pop cinema owners in good money.
The Reality: Due to distribution costs, many films make their money entirely off that overpriced candy that fat people noisily eat in the row behind you for the whole damn movie.