Expectation is linked to what we believe. Expectation influences how much effort we will invest in attaining our goals. It also influences how well we will be able to deal with challenging or stressful situations. Expectation is at work in every area of our lives. For example, in the area of health the placebo affect (taking a fake pill) shows how much a patient's expectation will influence the outcome of them getting better.
The thing to know is that if you have a strong positive expectation around acheiving something you will go the extra mile towards that end. Having a positive expectation will also help you activate the necessary inner resources to attain whatever you want.