Authors who write books create environments with their words. Summarily, they are usually less than useful at creating environments with lighting, placements, etc. There is usually tension when an author is called to write a screenplay, because the author wants to protect the literary merit of their work, but the director wants something that translates that into the screen. An inner monologue explaining one character's yearning for another in a novel can be expressed by one lingering camera shot on a look of desperation on that character's face, you know? And it has to, to fit in 118 minutes.

Anyways, directors are the ones who decide what lighting there is, who decide what mood music should be playing in the background, how close together the actors should stand, whether the shot should focus on their faces, or be a wider frame.

Basically, they are creating environments and lives.

No one's going to give James Cameron any awards for the story he told with Avatar, but for the environment he created? ~~