The expectancy model states that people are motivated to work when they expect to achieve things that they want from their jobs. It implicitly assumes that people make conscious decisions about which behaviors to engage in to satisfy their particular personal needs and goals.
The most important variables in the model are expectancy, which is associated with first-level outcomes; instrumentality, which is associated with second-level outcomes; and valence, which determines the desirability of a given second-level outcome.
According to the model, an individual must believe (expectancy) that effort in some activity will lead to some desired level of performance (first-level outcome), and that this level of performance will lead (instrumentality) to desired rewards (second-level outcomes with a positive valence).
Otherwise, the person will not be motivated to expend the effort needed to perform at the desired level.