Brothers

It is snowing outside, as well as in the book that I am reading, which is about a father and his sons in upstate New York. They're brothers. Neither one of them perfectly reflects their father's expectations, but the elder is better than the younger at hiding his rebellion, thus more the darling. Is there some unwritten rule of nature that there must exist this angel/demon dichotomy between brothers (siblings)? Why must the stories always be sad? I need to find a happy story with credibility, but I have a sneaking suspicion that all of the real stories are laced with a bit of tragedy. Is a happy story incapable of ringing as true to us, as believable and valid, as the sad, tragic tales do?