Following are some indisputably established facts.
Those on the left spend more time in formal education than conservatives do. They earn more money and spend more of their own money on themselves (and give considerably less of it to the needy, incidentally).
But they are much less happy than the conservative-minded, as the American social scientist Arthur Brooks illustrated in Gross National Happiness a few years back.
The left’s response was to cry “Of course! We have empathy and sadness in the face of injustice, whereas conservatives don’t give care and aren’t so troubled.” (see here, for example). This explanation, though very convenient to the explainers, fails to account for the left’s personal miserliness towards those less well off than themselves.
In NRO, Denis Prager posits several alternative explanations here. The whole thing is worth a read but this was the bit that stuck out for me :
Perhaps we are posing the question backwards when we ask why liberals are less happy than conservatives. The question implies that liberalism causes unhappiness. And while this is true, it may be equally correct to say that unhappy people are more likely to adopt leftist positions.
Life is hard for liberals and life is hard for conservatives. But conservatives assume that life will always be hard. Liberals, on the other hand, have utopian dreams. At his brother Robert’s funeral, the late Sen. Edward M. Kennedy recalled his brother saying: “Some men see things as they are and say, ‘Why?’ I dream things that never were and say, ‘Why not?’”
Utopians will always be less happy than those who know that suffering is inherent to human existence.
That this touches on ancient truth is supported by the following sayings of Marcus Aurelius:
Very little is needed to make a happy life
Adapt yourself to the environment in which your lot has been cast, and show true love to the fellow-mortals with whom destiny has surrounded you.
What sayeth The Rhetor?