Job, V., Dweck, C. S., &Walton, G. M. (2010). Ego depletion—Is it all in your head? Implicit theories about willpower affect self-regulation. Psychological science, 21(11), 1686-1693.

Much recent research suggests that willpower—the capacity to exert self-control—is a limited resource that is depleted after exertion. We propose that whether depletion takes place or not depends on a person’s belief about whether willpower is a limited resource. Study 1 found that individual differences in lay theories about willpower moderate ego-depletion effects: People who …

Isen, A. M., &Reeve, J. (2005). The influence of positive affect on intrinsic and extrinsic motivation: Facilitating enjoyment of play, responsible work behavior, and self-control.

[Two experiments demonstrated that positive affect fosters intrinsic motivation, as reflected by choice of activity in a free-choice situation and by rated amount of enjoyment of a novel and challenging task, but also promotes responsible work behavior in a situation where the work needs to be done. Where there was work that needed to be …