choices and motivation reduce happiness.

http://www.ted.com/index.php/talks/dan_gilbert_asks_why_are_we_happy.html
This talk is based on clinical research which pretty clearly shows the following (summerized in my own words):

• Choice opens the door for doubt regarding the choices you make
  
• Being highly motivated to make the best possible choices and reach the highest possible levels of attainment increases the chances that you will take risks and make sacrifices that will decrease your happiness.
  
• In a few months or a year, at most, you will be just as happy as you were before, no matter what actually happens to you.