It can also be a nightmare to see the printed words - words slaved over, fought for and won after battles with writer's block or missing muses - simply disappear because they lack importance to translate into the final moving picture product. OR, see that the finished product is so incomplete in what should have been included from the book that it resembles some cobbled together beautiful failure.
there are some novels that converted to the big screen in such a fantastic way - despite what had to be cut - that left viewers in awe and many readers satisfied with the end result. One example is the Lord of the Rings trilogy.
This was a trilogy with such a huge cast of characters, depth of history, and mountains of backstory that it was seemingly impossible to imagine anyone or any people crafting proper scripts, gathering just the right actors and actresses, and a director with a big enough vision to pull this off, But it happened. You can check out various interviews of the cast here because, well, it's just awesome.