7. Poorly Handled Love Triangles
Of all the reasons I list, this is probably the most well known. Love triangles are a shamelessly manipulative way of gaging your fandom's investment when writing a Young Adult novel, but they can work. See the Hunger Games for an example - If the characters are memorable, and the conflict manifests itself in a number of interesting ways throughout the plot, the actors and the story can make this threadbare subplot worthwhile as a small part of the main character's arc. Aye, there's the rub - it must remain a subplot, nothing more. When a movie tries to define a character by who they fall in love with, it is effectively giving up on making the character interesting in its own right. Twilight had a trio of main characters who were only defined by 2 things: they were all outsiders, and they were all into Bella. With barely a shred of notable difference between the writing of these characters (save their varied skin tones) there is no reason to be invested in their romance. In an example from last year, The Host tried to convince the audience that Melanie has an alien in her head, and the only defining difference between the two of them were the hunky boys they fell for. I hope I do not need to explain why this is characterization at its very worst.