“In short, we found that happiness depends not on how well you are doing, but whether you are doing better than expected. Our research shows how high expectations can be a problem. … Another reason that it’s hard to hack your happiness is that expectations are really important for decision-making. If you always expect the worst, it’s difficult to make good choices. When things go better than expected, that’s information your brain can use to revise your expectations upward so you make even better choices in the future. Realistic expectations are generally best.”
Know Thyself 