It can be, but in America they've been trying to give the father's that want custody of the kids their equal share. They do have a right to their children. The joint thing isn't really hard until they enter school, then it can get very difficult because the parent that moved out of the district will be required to transport child to school. But they no longer assume that the mother is the most fit parent. Unless proven otherwise, both are concidered equal until one is proven otherwise, and there can be some mud slinging going on there.