The short-lived nature of goal-based happiness

Our ability to imagine how something will make us feel is often flawed because of the impact bias. 

The impact bias leads us to overestimate the positive impact the accomplishment of a goal will have and underestimate how other events or feelings may influence the way we feel. After reaching a goal, you'll be happy for a short while, but despite reaching your goal, another goal will appear, and you'll assume that achieving the next goal will lead to more happiness. Yet, the list of goals is never completed.