Urie Bronfenbrenner, Two Worlds of Childhood: U. S. & U. S. S. R.

"Thus if we know a child has had sufficient opportunity to observe and acquire a behavioral sequence, and we know he is physically capable of performing the act but does not do so, then it is reasonable to assume that it is motivation which is lacking. The appropriate countermeasure then involves increasing the subjective value of the desired act relative to any competing response tendencies he might have, rather than having the model senselessly repeat an already redundant sequence of behavior."