I consider this to be one of the greatest fails of all time! If you are dedicated to literature, there should be no need for a movie.
The rule is: If you read a book before watching the movie, DON'T watch the movie.
Books are so powerful. A couple of words on a piece of paper can stimulate your mind, work up your imagination, and create thought. Unlike movies, you accept what is presented in front of you. [IMAGINATION IS NOT INCLUDED] Where is the fun in that?
I have read 'The Kite Runner', written by Khaled Hosseini, with no intentions of watching the movie. Due to a boring Sunday night, I found myself face to face with the characters I had just read in the book, but not quite the same. You see, you paint this image in your mind of how each character looks, interacts and the location the book is set in. When you watch the movie, you are erasing the image you created and have replaced it with a knockoff version of the book. I was highly disappointed with the outcome of the movie which seemed completely off, and valuable details that made up the beauty of the story were put aside, just like that.
Moral of the Story:
Movies do not give the book any justification due to a limit of an hour or so and having to cut certain parts and details you may find important. There is no time limit on reading a book. You read at your own pace and take in every detail the author wanted you to take in.