Making a film isn't just the case of hiring a couple of dashing actors, pointing the camera in their general direction and shouting action. If it was, Michael Bay would be unable to leave the house in the morning for all the Oscars and other assorted awards blocking his way.
It's exactly like what your teacher tried to drill into you at school; plan before you start. And this isn't just an essay on the usage of animal imagery in Of Mice And Men; the process of developing a movie is massive, and a substantial planning stage is essential for making the right decisions about story, character and tone. If a movie's flawed, you can normally trace the crucial issues back to a shoddy development stage (it's no coincidence that The Hobbit had limited pre-production under Peter Jackson after Guillermo Del Toro left).
Planning also allows the filmmakers the opportunity to get rid of the less-than-genius ideas that pop-up along the way. And make no mistake: a finished movie may be a masterpiece, but you can bet at least one of the earlier story treatments or drafts was utter cack, missing what made the finished film so great and making you question if anybody really knew what they were doing.
Here's eight movies where vastly different early drafts could have spelled disaster for future greats.