Looking through Ran Prieur's site earlier, and came across this article.
This part really caught my attention:
To Hell With Happiness
In the united states, people rank happiness as their most important goal. That view has a special impact on introverts. Happiness is not always their top priority; they don't need external rewards to keep their brains in high gear. In fact, the pursuit of happiness may represent another personality-culture clash for them.
In a series of studies in which subjects were presented with an effortful task such as taking a test, thinking rationally, or giving a speech, introverts did not choose to invoke happy feelings, reports Boston College psychologist Maya Tamir. They preferred to maintain a neutral emotional state. Happiness, an arousing emotion, may be distracting for introverts during tasks. By contrast, extraverts reported a preference to feel "happy," "up," or "enthusiastic" and to recall happy memories while approaching or completing the tasks.
At this year's meeting of the Society for Personality and Social Psychology, Tamir, along with Iris Mauss of the University of Denver, presented a paper entitled, "Come On, Get Happy: The Ironic Effects of the Pursuit of Happiness." The two did not specifically study introverts or extraverts. What they discovered is that, for all people, the pressure to be happy actually reduces happiness.
"We found that when we prime people to value happiness more, they become more unhappy and depressed," reports Mauss. "Our findings offer an intriguing explanation for the vexing paradox that even in the face of objectively positive life circumstances, nations generally do not become happier."