Most of us spend our lives chasing happiness. We constantly look at things we 'need' in order to be happy. However, according to the research in this video, this is missing the point. To a substantial degree, we can manufacture happiness in our minds by simply accepting things. Those 'grass is always greener' people live in perpetually misery, as they constantly chase something which is 'better' instead of enjoying what they have right here and now.
Interestingly, Dan in the video, shows his findings that after a year, both a lottery winner and a person suffering a disabling accident, return to being as happy as they were previously. To me this says that most of happiness is ultimately all in the mind.