There’s usually a climate of excitement and criticism around film adaptations. An adaptation is a film that is made from a book, or even a short film, as was the case with Whiplash. Writing an adapted screenplay can be much like writing spin-offs and sequels. The world and characters are already created; all that’s left is transforming the story into screenplay format.
Some difficulties arise when adapting a novel into a screenplay. Protagonists have internal monologues in novels, but writing a page long voice-over of someone’s thought process is not necessarily what the screenwriter wants to do. The screenwriter ends up using different visual cues to show what the protagonist is thinking: facial expressions, visual symbols and metaphors, and if absolutely necessary, one sentence that sums up their thoughts. So, not only do the characters, world, and story need to be accurate for fans of the novels being adapted, the characters’ emotions need to be transferred from expressive novel writing to descriptive and concise screenplay format. (I only say concise because one page of a screenplay is typically supposed to equal one minute of screen-time). This is a reason why narration is typically avoided; if you can’t see it, don’t write it.
The pressure of making sure the novel is accurately adapted is trumped by knowing the fans will enjoy a visual representation of a beloved novel. Of course there will be criticism around every film, but that is to be expected when the narrative of the film can be compared so readily to the narrative of the novel.