Victor Vroom proposed the Expectancy theory of motivation. This theory is basically an attempt to come up with a model of how people would rationally decide whether or not to be motivated to pursue a particular course of action.

The three main factors of this theory are Valence, Expectancy, and Instrumentality.

Valence is the importance placed upon the reward. Expectancy is the belief that efforts are linked to performance. Instrumentality is the belief that performance is related to rewards. For example a salesman's expectancy is his belief that more number of phone calls (effort) will result in higher sales (performance). His instrumentality is that higher sales (performance) will result in higher commissions (rewards). His valence is the importance attached to the commissions (rewards).

These three factors result in motivation. If any one of these factors doesn't exist then motivation vanishes. If the salesman doesn't believe greater effort leads to performance then there is no motivation. Similarly, if commissions don't increase with sales then instrumentality disappears.

According to the expectancy theory the amount of effort people exert on a specific task depends on their expectations of the outcome.