Social scientists have determined that we accept inner responsibility for a behavior when we think we have chosen to perform it in the absence of strong outside pressures. A large reward is one such external pressure. It may get us to perform a certain action, but it won’t get us to accept inner responsibility for the act. Consequently, we won’t feel committed to it. The same is true of a strong threat; it may motivate immediate compliance, but it is unlikely to produce long-term commitment.
