Why are we so bad at predicting our future happiness?

From Eurekalert:

The new evidence comes from Jordi Quoidbach, a psychological scientist at the University of Liege, Belgium. Quoidbach and Elizabeth Dunn, his collaborator at the University of British Columbia, found that our natural sunny or negative dispositions might be a more powerful predictor of future happiness than any specific event. They also discovered that most of us ignore our own personalities when we think about what lies aheadâand thus miscalculate our future feelings.

And:

“It might be worthwhile, before you make a big decision, to think about your personality and how you usually react,” Quoidbach says. Think about planning a vacation, for example. If you have a happy disposition, you probably don’t need to waste a lot of money and effort finding the perfect location (because you will be happy with most vacations anyway). By contrast, if you have a less happy disposition, you might be more prone to regret the slightest annoyance, so carefully planning every detail of the trip might be the best strategy for your future happiness. “Don’t focus too much on the event; think about who you are,” advises Quoidbach.