The above title is something I've heard multiple times from screenwriters and producers -- and now I'm getting to experience it first hand! Essentially, it all comes down to contracts. The fights over contracts, money, credit, back-end, and so on, get rather crazy. I imagine this is true in any business but there is one complicating factor in Hollywood: people don't have a standard payscale.
When you're starting out, frankly you'll agree to practically anything in order to get a produced credit, and the companies cutting the check know that. However, most people also have a thorny sense of justice that rears up when they feel like they're getting shafted. I have no complaints about my contract; I didn't expect much and actually got a bit better deal than I anticipated. But I know there have been some fights elsewhere.
Another way the no-standard-payscale comes out is that established actors, directors, and writers, charge based on the kind of movie being made. They don't have a standard salary. So, even though Tom Cruise might typically make 25 million per picture -- that doesn't apply if it's one of those prestige roles with Oscar aspirations. You can get actors for scale on those. So that means that arguments also arise over whether or not the movie is commercial or prestige.
Anyway, I received my first check yesterday, really just a deposit (i.e. an option payment) -- but already more than I made combined doing RPG writing. So tonight I'll fulfill my promise to myself and go out and buy the Stanley Kubrick Collection -- that's something I held off on since I wanted to purchase it with screenwriting cash.