Unmet expectations, no matter how small or unimportant, are enough to put us off. Brain research on expectations shows that dopamine cells in the brain fire off in anticipation of primary rewards. When a cue from the environment indicates that you will get a reward, dopamine releases in response.

But if you're expecting a reward and you don't get it, dopamine levels fall drastically. This feeling is akin to pain. Expecting a pay rise and not getting one can create a funk that lasts for days.

Good levels of dopamine in your prefrontal cortex are critical for focusing.

Positive expectations increase dopamine levels in the brain, and these increased levels make you more able to focus. Teachers know that children learn best when they are interested in a subject. That interest, desire, and positive expectations are variations of the increased level of dopamine in the brain.