In a comparable way balance theory is useful in some contexts, but not all (If Jack likes Jill and Joe likes Jill, Jack does not necessarily like Joe (Newcomb, 1971)). Exchange and interdependence theories must take cognizance of the differing properties of the resources exchanged (Foa & Foa, 1974) and of the fact that what is considered as fair differs between relationships of different types (Lerner, Miller, & Holmes, 1976) and, in children's relationships, with the age of child (Leventhal & Lane, 1970). Principles of negative and positive feedback are valueless unless we know which operates in which relationships in which circumstances.