Why should I feel a strain to reciprocate a concession? The answer rests once again in the benefit of such a tendency to the society. It is in the interests of any human group to have its members working together toward the achievement of common goals. However, in many social interactions the participants begin with requirements and demands that are unacceptable to one another. Thus the society must arrange to have these initial, incompatible desires set aside for the sake of socially beneficial cooperation.
