... to provide an easy way out for people who couldn't be bothered to read the book; to provoke people who didn't have time to read the book to make some time; and to annoy the people who have actually read the book.
Maybe it's just me, but I can't watch a film based on a book I've read without noticing every little thing (or person1) that has been left out or altered.
So Why Do They Do It?
For the people controlling the funding of the film, who obviously have ultimate control, films based on books are a safe bet2. Any book with an 'established fanbase', as the media people tend to call it, will attract a reasonable number of people to come see it, and the various tie-in versions of the book will ensure that they at least break even. Yes, people will actually buy a copy of a book they already have, just because it has pictures from the film on the cover.
Forget that these people already know how the story goes, they're looking for the interpretation. And the casting of the characters. And the opportunity to emerge knowing that, in at least one very important way, they could have done it better. I know. I speak as a person who regularly leaves films saying 'He looks too old/young/hairy/skinny to be XXX'. (often to find out that the actor is in fact older than he looks, and that the book doesn't mention facial hair or Body Mass Index - maybe more books should take up this practice, it would certainly make life easier for the filmmakers).
Why Must We Feel This Way? Why Can't They Just Get It Right?
A major problem in the translation is that books are bigger than films. By this I mean that an ordinary-sized book, even one heavy on description, even when a picture is worth a thouand words, will still need significantly more than the average length of a film to incorporate everything. So filmmakers are forced to cut whichever bits they feel they can get away with, to keep the film within the reach of the attention span3 of the average cinema-goer. Which leaves people like me to come out of a film, blinking into the unaccustomed daylight, crying 'But what about the...'
Rewards For The Hard Work
For this reason I have come to think that it is impossible to create a film from a book whereby all the people who have read the book will agree that it is 'right'. So I am proposing a new set of awards, for actors who have portrayed characters from books I have read in a way that was as good as (or better than) I imagined4. There would also be a mention for the director, and for the person in charge of casting the winner in that role.
My first three nominees would be Anthony Hopkins, Alan Rickman, and Viggo Mortensen. Votes, other nominations, and guesses at what roles these three were nominated for5 are all welcome.
A slightly less biased, but more example-ridden, examination of this phenomenon can be found at Films Based on Books.