Locke (goal setting theory) (1967)
This theory is based on the observation that motivation is much harder to achieve when procedures are established and more importantly when individuals are challenged and stimulated on objectives without too many constraints, which we might call a constraint of result without a constraint of means. We're at the crossroads of self-determination, expectation, and a sense of accomplishment.

The point is, and remains, to ensure that the goal is achievable without being too easy. The goal must be clear and precise. And preferably defined with the participation of the employee (or team). Ongoing feedback must enable the individual (or team) to see where they stand in their progress.

Finally, being given such a challenge positively affects self-esteem, as it is a sign of the confidence the company places in the employee (or team).