The 40%: Your happiness is up to you.
50%, 40%, 10% — these are the cause/effect ratios at which positive psychology research tells us results in our happiness.
The 50% is fixed at birth through our DNA and thought to be stable over time, immune to influence or control. Life circumstance is the 10%, which is the good or bad that 'happens to us' in existing. Finally, the 40% of our happiness come from our actions or exercises that require some degree of daily personal effort— Intentional activities.
Changing the game
With that 40% we already possess the tools necessary to be our own personal game changers. Although we don't have control over genetics and life circumstances, the third factor, intentional activity, is arguably the most hopeful and promising means for altering our perspectives and life.
Helpful Articles
Happiness - 50% genetics, 10% circumstances, 40% intentional activity - http://www.lifecho.com/happiness-genetics-circumstances-intentional-activity/
Sonja Lyubomirsky and the How of Happiness - http://www.edbatista.com/2009/02/happiness.html
Michael Strahan Wakes Up Happy - http://www.livehappy.com/lifestyle/michael-strahan-wakes-happy