Sibling rivalry. Sometimes, a kid just isn't ready for some little squirt to come along and invade his space, his own room. So what if there's an extra bed in the room; isn't that where the stuffed animals are supposed to sleep?
How could a couple of otherwise sensible parents just bring a new kid home without even consulting their very own son? Still, a younger sibling can be in need of a big brother's guidance. And a big brother, even if not so very big, can have a lot to offer once he gets used to the idea.