One of the more depressing pieces of advice I've seen come out of a successful author's mouth while they were wearing a straight face was something along the lines of, "Don't put anything on the page that can't be easily filmed, because you don't want to scotch any potential movie deals for your work."
From outbursts come truth, it seems. Not in the sense that the highest aspiration for any written work is to become a Hollywood meal ticket for its author, but that the things people say with straight faces tell you a hell of a lot about where their hearts really lie.
Some time back I found myself in a conversation about movie adaptations of novels, and I made a point which seemed second nature to me but ended up being roundly disputed by some of the folks in attendance: that there are things you can do in a novel that you can't do in a movie, and vice versa, and vive la difference. You don't want them to do the same things. You get a different set of experiences, both qualitatively and quantitatively, from reading any book than you do from watching someone's filmed interpretation of that material.
Reading engages the imagination differently. It forces the reader's suspension of disbelief to do more of the heavy lifting. You and I did not imagine seeing quite the same man when we read about Paul Atreides, and that is what makes reading Dune interesting for both of us: it makes our individuality all the more pronounced and fruitful. The fact that we got such different things out of the same words on the same page is a way to discover who and what the other person is.
Now, I won't argue that a movie has similar pleasures of interpretation — I wouldn't have written umpity-hundred movie reviews on this blog if I didn't! — but the way we use our imaginations to interpret both kinds of work need to be exercised separately. Hence all that talk of getting the movies out of the English Lit courses: the last thing we need is to give people yet another excuse to not actually read something on its own terms. I don't mind when a book I love gets filmed, but what gets put on the screen because of that isn't meant to put an end to how the book can be brought to life in one's mind.
But from the way some people talk about books, you'd think that was the idea.
The other downside, one less obvious, to thinking that any book is just fodder for a film-to-be, is how it subtly — or maybe not so subtly — discourages authors from working on anything that isn't easily filmed. By that standard, most anything from Proust to Kafka, and even F. Scott Fitzgerald, would have never been penned in the first place.
Fitzgerald in particular comes to mind because of how deceptively simple his writing is, and yet every single movie version of The Great Gatsby (Baz Luhrmann's, doubly so) has failed because the book is not about what is directly on the page. Vonnegut, too: you can't really film something like Slaughterhouse-five, because again so much of what the book is lies somewhere between the page and the reader. That didn't stop director George Roy Hill from making a very noble attempt of that book all the same, but the resulting movie is still more of an oddity than anything else. The book succeeds because it's not bound by the literalness film imposes on its subjects. When we're told that Billy Pilgrim has been kidnapped by aliens that look like plumbers' friends, it's not the same thing as actually being shown it.
Vive that particular difference, says I.
It says something that some of the best films made from books have not come from particularly distinguished source material. The better a book is as a book, the harder it is to render it as something else. Here and there, you have exceptions -- The Accidental Tourist, The Year of Living Dangerously, The Maltese Falcon, A Clockwork Orange (only Kubrick could have pulled it off, I'm telling you), The Quiet American -- but they're rarities. Almost never do you come across a book that is a satisfying literary experience for the same reasons it films well.
In that respect, then, the fellow I quoted up above was completely right. Books that film well put all their action on the page, and thus save the filmmakers the work of having to figure out what to keep and what to toss. With your average Michael Crichton or Tom Clancy novel, the biggest problems involved in adapting them were logistics: how do you condense all those plot threads into a two-hour movie? With John le Carré, you could keep the plotting, but then you'd have to lose all of his bitter, wry observation, the sort of thing that becomes clumsy and overweening when turned into voice-overs or the like. Fight Club pulled off such a thing, but I fear at the cost of setting an example few other movies ought to emulate.
From all this I'm seeing another motive for producing one- and two-dimensional work. Books where all the action is on the page the only kinds of books worth writing, because they're likelier to be filmed, and thus get far more of an audience than most any book sees in its lifetime. If you want to be read, so goes the thinking, you've got to write to be seen — or, rather, filmed.
Cynicism is too nice a word for such thinking. It borders on nihilism, the nihilism that is convinced works of genuine imagination are "too difficult" for people, that the author should not "confuse" the reader, and that the only works worth writing are the ones that find the broadest (and thus flattest, and shallowest) possible audience. Such are the thoughts of people who are afraid of words, who have contempt for those who wield them as a liberating cultural force instead of as a soporific to fill downtime.
Sum of comment: "Unfilmable" is not an insult. In this day and age, it might well be some of the better praise to be bestowed.