There’s some really interesting stuff about Greene’s process in Alexander Mackendrick’s On Film-making. In particular, he reveals that he wrote The Third Man first as a novel without the intention of ever publishing it. Here’s Greene:
“To me it is impossible to write a film play without first writing a story…One can reproduce the an effect caught in another medium, but one cannot make the first act of creation in script form. One must have the sense of more material than one needs to draw on. The Third Man, therefore, though never intended for publication, had to start as a [prose] story.”
I can see a lot of benefit of this process, what do you think?