According the B628 course book, Expectancy Theory, proposed by Vroom (1964) is a well-regarded theory of motivation. It’s central premise is that we act expecting certain outcomes, based on our past experiences. Vroom argues that it is not just the promise of a reward that is motivating, but instead, the link between effort and reward.
Rewards must be in line with effort, and the reward must be seen to be achievable in order for the reward to be motivating. Conversely, costs must also seen as avoidable in order for them not be demotivating.
In short, the links must be clear and strong for a reward or cost to have a motivating or demotivating effect.
The assumption is that the person being motivated or demotivated actually wants the reward, or wishes to avoid the cost!