When you watch movies do you think about how they were made? Are you analyzing them as you’re watching or are you suspending your disbelief for the moment and just fully submerging into the world of movies?
Sometimes the success of the whole movie or movie franchise depends on the right casting of the main characters, especially with book and comic adaptations.
When we are watching movies, we sympathize with heroes and are hating on villains especially if actors playing them are really good at portraying the character. It becomes hard to believe that real people are different from their on-screen counterparts and actually better then they are.