Cressida Cowell said this quote

Please do not blame the story.The story cannot help itself. We do not realize it at the time, but sometimes the story we are all a part of is not just a story about Vikings and islands and dragons. It is a story about growing up.And one of the things about growing up, one of the inescapable, inevitable laws, is that one day...One day... one day... It is going to happen. I am sorry, but it's true.