It's commonplace to think that if we can become successful, then we will be happy. Harvard lecturer and "positive psychology" researcher Shawn Achor says we have that backwards, that it's far more accurate to say that happiness precedes success.
The psychology of happiness is Shawn Achor's research specialty. Achor says that recent psychological and neurological research shows that our performance is measurably better at our work or other pursuits when we are happy than when we are even neutral, that we are more intelligent and we are more creative. And the good news is, we can in a matter of weeks retrain our brains to make ourselves happier and, consequently, more productive.
Achor lectures on the subject of positive psychology at Harvard, where his class on the topic is said to be the most popular offering on campus.
I highly recommend his TEDx talk which I have embedded here.