Books and films both tell stories, but what we want from a book can be different from what we want from a movie. Is this true for you? If so, what’s the difference between a book and a movie?
Books and movies and movies are completely different mediums. A book literally tells you a story; someone is talking to you. You hear the words in your head and they invoke the pictures in your imagination. They can take the time to unfold slowly, letting the language and story wash over you. There are really no limitations of length. They can take 100 pages to tell the story or 1000.
Movies, like I said, are another medium. They have, at the VERY most, three hours to tell their story. And that length is reserved for the hugely anticipated blockbusters like Lord of the Rings or Star Wars. A normal movie is only about two hours. When you're translating a book to a movie, if it's a full novel as opposed to a short novel or novella, that's hard. Close to impossible. 1 page of script in a screenplay is supposed to equal roughly 1 minute of screen time. So think about it. A movie is 2 hours long, so 120 minutes. That's 120 pages. How many novels are that short? Of course things are going to be left out. A book can tell you the back story, can delve into deep psychological character development, can tell you how a person feels about their current environment. A movie has to show that.
It's hard to compare a movie and a book. A movie takes a novel and instead of making that novel into a play script by reading it line for line, they take the characters, the events, and themes that are discussed and go from there. The movie is it's own story. The movie is an interpretation of that story.
I think I kind of rambled a bit in that answer. I got interrupted a few times while writing it (seeing as I am at work). But hopefully I got the idea across.