The reason? Well, I like to pride myself in having a good imagination. This is a real blessing when reading a book. There was may a time when I was younger that I went to sleep imagining myself in my favourite book. I used to dream up new adventures, imagine what I'd do differently. And all the time I'd have a vivid picture of what the characters looked like. The observant of you may now have seen my problem- what if the movie casting doesn't live up to the image I already have?
Also, if I haven't read the book already then I feel that seeing the movie first can really spoil my reading experence. I can't always picture the actor doing what's on the page, nor can I enjoy using my imagination in the same way. Plus, somehow those pages become less of an escape from realism.
There are exceptions to this rule of course. I simply loved Northern Lights- the film being even more exciting than the book, the whole series of which I enjoyed. I think the key with this one was that it still kept the feel of the book, the basic outlook of Phillip Pullman.
And when it comes to Harry Potter I've never really enjoyed the books. This could be because I tried to read the first one after watching several of the films (see above), but I have a feeling I probably wouldn't have liked them anyway- something I can't quite pin down to do with the writing style. Of course, all this means that I could enjoy the movies totally guilt-free.
Despite all this I somehow feel obliged to watch film of books. When people rave about them then I generally read the books quickly if I haven't already before going to the cinema (I intended to do this with War Horse but, due to a cold, never actually got to a screening). Other times I'll get it out on DVD after I've done my reading. It could take me a while to actually getting round to watching it however (The Time Travellers Wife is waiting for this treatment).
When it comes to The Hunger Games I'm unsure what to do. I have the original book sitting on my shelf. I've heard the hype. But yet something is stopping me from either reading or watching. I wish I knew what it was.