In a comment on this entry, Thom writes,
I’m not convinced that what we call happiness is a single thing. We could probably divide it into (at least) two concepts – local happiness “this instant” and general happiness. I think that having children relates more to the latter (or possibly towards a related concept like fulfilment).
Beyond that you’d need a theoretical account of happiness to make sense of what’s going on. The (naive) economic analysis is that happiness leads to inaction, but the some theories of emotion propose the opposite (with evidence in support). For example the broaden and build theory of emotion proposes that the evolutionaty function of positive emotions is to build resources – so you’d maybe expect happy people to plan for the future (whereas we know very unhappy people don’t).
I’m especially interested in his second comment–the point about action and inaction is something I’d never thought about. From an economic standpoint, if you are at a maximum of relative happiness, you would want to do what it takes to stay there (which might be inaction, but it might be to work your tail off, if, for example, you’re happy but in major dept). For unhappy people, one could try a reverse explanation: if you’re unhappy despite everything you’ve tried, then maybe giving up seems like the best alternative.
The explanation given by Andrew matches evolutionary psychology explanations of why unhappiness leads to inaction. The example commonly cited is of monkeys trying to climb the social ladder, which is done by fighting the monkeys who are higher up the ladder. If you're fighting and losing, you should stop. And nature does this by making you unhappy. Paul Gilbert writes about this in his book Depression: the evolution of powerlessness.
Does that mean that happiness is just chronic frustration?