Acting, direction, production and just whole films rest on getting one idea and doing it right. If you do, you have a chance at a classic. If not, it may never get made.
The idea has to come first. It's just not always the slog that you expect. William Goldman says he was sitting around a campfire, listening to a true story: "And I clearly remember that I turned to Ilene... and said something I had never said before: 'That's a movie'". It was "The Ghost and The Darkness" and it flopped twelve years later."
It's common for ideas to take years to get going, sometimes because you can't convince anyone to buy it, sometimes because you can't figure it out. "Star Wars" crawled out of George Lucas's mind and Anne-Marie Martin spent at least two years trying to convince her husband Michael Crichton to write "Twister" about tornadoes with her. "It's a great idea," he would tell her: "But what's the story?"
You can argue that everything beyond the first notion is really development. And it's true that some of the most famous films were thought up extremely quickly. "I've always wanted to do a chase across the face of Mount Rushmore," said Hitchcock to screenwriter Ernest Lehman and suddenly they've got the core of "North by Northwest".
Similarly, "Alien" and "Total Recall" were each thought up in an afternoon - the same afternoon. By the same people.
We all have ideas for films but these are the ones that made it through wishful thinking and onto the big screen. If the writers knew what lay ahead of them, though, they'd switch to radio immediately.
Read how George Lucas thought up the idea for "Star Wars" in "Factory Line Part 1 Sidebar - Star Wars"
Go to Factory Line - Part 2: I've Got This Great Story, George Clooney's Practically Signed
Factory Line - Introduction
Factory Line Glossary
Sources:
"The Ghost and the Darkness", William Goldman, Applause Books, 1996 ISBN 1-55783-267-6
"Which Lie Did I Tell?", William Goldman, Bloomsbury, 2000, ISBN 0-7475-4977-X
The "Alien" Legacy DVD
Internet Movie Database
"Twister", Michael Crichton and Anne-Marie Martin
"Star Wars" history, William Gallagher,