Study: Extroverts are happier, Introverts should act like Extroverts to feel happier?

That's the study (WSJ). I get the idea that moving outside your comfort zone has its rewards (there are studies for that too! NYT) - but that Extroverts are more motivated because of their sensitivity to dopamine? On the other hand, motivation and productivity (actually getting things done) I suppose aren't the same thing.