Have you ever been the less favorite? It doesn’t feel good. It can urge you to jealousy and anger which can lead you to hurt the favorite or at least to want to.
But then consider why the other is favored: more loving and caring more attentive less self-centered?
Or is it the favored one just better-looking or genetically given?
Whatever the case, jealousy and hurt can send me down a crooked path and make me miserable.