Right. Movies don’t come out of thin air. They all need inspiration whether a book, a story, news item, etc. Its not writers making movie scripts ala SNL sketches.
I'd say all art needs inspiration, but there are certainly plenty of screenplays (just like theater plays) that don't come from a single item. As a random example, Woody Allen came up with the title "Midnight in Paris", then wrote the whole screenplay from the title.
