Many movies have a dedicated following of fans. However, often the most popular movies began in writing. They began as books. Many books are taken off of the page and turned into images on the screen for viewers everywhere to see. Examples such as Twilight, Harry Potter, and Lord of the Rings can be used to demonstrate how a popular book franchise can turn into a box office hit overnight.
Twilight was published some time before it got popular, and that popularity of the pages turned into a devoted fanbase for the movies. Harry Potter books were released before the movies, and it wasn't unusual for fiction fans to line up around the block waiting for the release of the newest book.
However, often times many fans of the book are disappointed by what they see on the screen. This is because the books are (almost) always better than the film. Movies normally have a time limit, and they can only incorporate so much detail before the audience gets restless.
Recently, movies have become longer in order to stick to the book, and audiences have become more patient to sit in their seats. This still has not rectified the situation where the books are better. Books have more detail, more description, and they take the reader with them into the story. Movies have the visual aid, but they can't give as much detail or explain what's going on in that characters head as well as the written word.
This does not mean you should read the books and boycott the movies. It mean appreciate the books first, and take the movies for what they are.
