Adapting a beloved book into a movie is a difficult, precise operation, like re-entering the atmosphere in a space shuttle, or making porridge for Goldilocks. You have to get it just right, balancing demands for fidelity to the source material from the book’s devoted fans while also making sure the film stands on its own merit and tells its own story. Cater to the fans too much, and you turn the book into a lifeless theme park ride that has all the right things for devotees but barely makes sense to new viewers.