"The effects of external interventions on intrinsic motivation have been attributed to two psychological processes:
(a) Impaired self-determination. When individuals perceive an external intervention to reduce their self-determination, they substitute intrinsic motivation by extrinsic control. Following Rotter (1966), the locus of control shifts from the inside to the outside of the person affected. Individuals who are forced to behave in a specific way by outside intervention, feel overjustified if they maintained their intrinsic motivation.
(b) Impaired self-esteem. When an intervention from outside carries the notion that the actor's motivation is not acknowledged, his or her intrinsic motivation is effectively rejected. The person affected feels that his or her involvement and competence is not appreciated which debases its value. An intrinsically motivated person is taken away the chance to display his or her own interest and involvement in an activity when someone else offers a reward, or commands, to undertake it. As a result of impaired self-esteem, individuals reduce effort.