One of the frequently-cited conclusions from positive psychology research is that happiness results from a combination of genetics, circumstances, and voluntary activities. This is reasonable enough - indeed, it is a virtual tautology that applies to most any human characteristic.
Some positive psychologists go further and propose a happiness formula, typically a weighted sum of its components, with weights based on research with large samples of individuals. A representative set of weights is 50% genetics, 10% circumstances, and 40% voluntary activities. Again, this is reasonable enough, reflecting the research literature as I read it, although the exact weights are always a function of the samples from which they are derived.
So where am I going? To the conclusion that it is thoroughly unreasonable to think that we can parse the happiness of an individual, in the moment or in general, in the same way that we can parse the happiness of samples of individuals.
For people in the aggregate (a sample), we can perhaps say that 50% of the variation in their happiness is attributable to genetic differences. But we cannot say that Joe's short-term happiness following a raise at work or the victory of his favorite sports team or a wonderful weekend with his family is 50% due to his genes. That makes no sense. Which 50% are we talking about? The first 50%, the second 50%, or some other 50%? This is a category mistake of the first order.
I am reminded of the old question, "Which contributes more to the area of a rectangle - its height or its width?" We can readily see that this is a silly query. Sure, given a "sample" of rectangles of different sizes, we can provide an answer that summarizes the sample as a whole. But we would not expect the "weights" to generalize to other samples of rectangles, and in any event, we know that for given rectangles, the answers might vary widely.
The exact same point applies to thinking about happiness and its determinants, even if the point is harder to grasp.
Let's start with genetic influences. The technical meaning of the heritability of a characteristic is the proportion of its variation across people due to variation in genetic factors across people. Heritability estimates (like the 50% happiness heritability figure) therefore apply to groups and not to individuals.
Along these lines, please do not equate heritability with any simple notion of inherited. Perhaps we can say that Joe inherited his blue eyes from his mother*, but we cannot say that he inherited his happiness from her ... of half of it ... or any of it for that matter.
The same argument applies to the other components of happiness and their weights. So, "circumstances" include the nation where one happens to live. If the weights are based on a comparison between, for example, Norway and Sweden, the conclusion would follow that where one lives matters little. But if the weights are based on a comparison between, for another example, Scandinavian nations and sub-Saharan African nations, then the weight accorded to circumstances would be much larger.
Moreover, we cannot say how much of the happiness of a given person results from the nation in which he or she happens to live. We can only offer generalizations about groups of people.
It is not clear to me whether positive psychology authors who present such formulas intend these formulas and their weights to apply to individual people or to the specific moments of happiness that individuals experience. I do know that their readers often make these leaps because I encounter this notion with incredible frequency among my students who have read popular trade books on happiness. I spend a lot of time trying to explain heritability to them.
Ed Diener (2008) made the same point in his important discussion of the "myths" of happiness, under the heading "Myth 2: The causes of well-being can be understood as a pie chart of influences." He used a great example that I have found useful - mortality. It is possible to say, for a sample of individuals, what the typical causes of death are: cancer, stroke, accident, murder, malaria, and so on. Some causes are much more likely than others, and these can be deemed the more important causes of death - for the sample.
In most parts of the world, malaria does not lead to a large percentage of people's deaths. But that is little comfort to the person who happens to die from malaria, and it would be foolish for someone who lives in an area where malaria does occurs, however infrequently, not to take appropriate precautions.
As Diener (2008, p. 499) concluded:
These figures [weights] are sometimes offered to the public as a guide to what might be most worthwhile to change in order to achieve greater happiness. However, the causes for change in an individual's happiness might diverge from what causes differences in happiness between individuals ... one person might gain an enormous boost in happiness from becoming religious, even if the amount of individual differences in due to religion in a population is modest ... The pie-chart way of thinking is seductive, because it is clear and simple, but ... [it can be] ... misguided.
Positive psychology is important because it is based on research. But the research needs to be understood correctly.
* I believe that the "inheritance" of eye color, although a familiar example, is hardly this simple, so just appreciate the larger points about the heritability of happiness.
Diener, E. (2008). Myths in the science of happiness, directions and for future research. In M. Eid & R. J. Larsen (Eds.), The science of subjective well-being (pp. 403-514). New York: Guilford.