As it turns out, people are not very good at predicting what will make them happy and how long that happiness will last. They expect positive events to make them much happier than those events actually do, and they expect negative events to make them unhappier than they actually do. In both field and lab studies, we’ve found that winning or losing an election, gaining or losing a romantic partner, getting or not getting a promotion, passing or failing an exam—all have less impact on happiness than people think they will. A recent study showed that very few experiences affect us for more than three months. When good things happen, we celebrate for a while and then sober up. When bad things happen, we weep and whine for a while and then pick ourselves up and get on with it.

The Science Behind the Smile - Harvard Business Review