This has been described as a self-help book for people who don't read self-help books. It might also be described as a popular science book for humanities graduates. It is a readable but carefully documented discussion of ideas and insights in the field of positive psychology - the branch of psychology which seeks to promote human flourishing rather than merely to treat mental disorders.
People's "affective style" - how happy and optimistic they are - tends to be broadly fixed, and is to a considerable extent genetic (it seems to have something to do with the structure of the frontal cortex). Haidt is saying nothing new here - this phenomenon has been the subject of research for some time, and it was first identified by Adam Smith in the 1750s. The literature attests that, when people experience major positive and negative life events, such as winning the lottery or becoming physically disabled, their level of happiness tends to re-align, as time passes, with its previous long-term average.
This is not mere biological determinism, however. Haidt notes that it is possible to change one's fundamental affective style, if not always easy. In particular, it can be done using ancient wisdom (meditation), modern psychotherapy (CBT) or chemicals (Prozac). Moreover, leaving aside one's genetic inheritance, happiness does have some components which relate to changing circumstances and behaviour. The reported relationships, however, are not what one might expect. In particular, increased wealth makes only a small difference once a person is above the poverty line - and spending money only seems to increase happiness when it is spent on activities and experiences rather than material objects (Haidt suggests that this is because experiences offer opportunities for interpersonal interaction and bonding). Membership of "privileged" social groups doesn't count for much either - white Americans are only slightly happier than black Americans, attractive people are no happier than unattractive people, and men are no happier than women.
What does make a difference? Haidt notes that sages such as Buddha and the Stoics of ancient Greece recommended losing all attachments to worldly things. He argues that this approach, while partially correct, goes too far. We can't and shouldn't cut ourselves off from the world. Haidt's answer to the question of how to live a fulfilling life echoes that of Freud - lieben und arbeiten, to love and to work. Human relationships recur
as a candidate for happiness-enhancement both in the academic literature and in sources of traditional wisdom: the advice given by sages like Buddha, Jesus and Confucius can generally be boiled down to the interpersonal dynamics of reciprocity or love. As for arbeiten, this might be achieved by those who see their work as a vocation and who do their work in a way that plays to their natural strengths. Finally, Haidt also notes the importance of having a connection to something larger than oneself.
To some extent, the quest for happiness is obstructed by our evolutionary heritage. Haidt notes that we have an inherent "negativity bias" - for obvious evolutionary reasons, we react much more quickly and strongly to perceived threats than we do to perceived advantages. Nevertheless, perhaps surprisingly, most people seem to have a generally positive overall affect. Haidt refers here to Robert Biswas-Diener's cross-cultural research, which has ranged from the Inuit in Greenland to prostitutes in the slums of Calcutta, via the Vatican and Dubai. Across classes and cultures, Biswas-Diener's experimental subjects consistently report that they are more satisfied than not with their lives.
This is a very interesting and useful book, although it is rather long in parts and tries to do rather too much. In particular, large tracts of it deal with issues which are not central to positive psychology and which are dealt with in greater detail in Haidt's later book The Righteous Mind (motivated reasoning, the psychological basis of morality, etc). Nevertheless, I would recommend this book to anyone interested in the psychology of happiness, even if they are scientifically illiterate.