Another French psychiatrist that wrote inspiring books about happiness: Christophe Andre.
In his opinion, human beings are unhappy by nature. The cause is evolutionary: in the past we always had to be alert for and worried about threats. According to him, it takes hard work to be happy. Two important things to achieve happiness, besides food and a home, are social bonds and contact with nature. And last but not least: to be able to enjoy the small things in life and to live in the moment because we never know what tomorrow brings...
See his website for more information (albeit in French):
http://christopheandre.com/