One contributing factor I can point to is that I've been thinking about the problem of happiness and the hedonic treadmill for some time.
It's also true that my father passed away while I was still fairly young, so I had the impetus to consider his life in its entirety and to evaluate which of the things he did really mattered, and which didn't.
If you're interested in optimizing your own life satisfaction, I recommend the Happiness Project blog, written by Gretchen Rubin (she is Robert Rubin's daughter in law; I once worked with her husband who was at the time an investment banker). I especially recommend her short movie The Years Are Short (it's only a minute or so long) to any parent with small kids.
I guess I would describe myself as something of a stoic. My favorite bit of advice for academics comes from...
"Or does the bubble reputation distract you? Keep before your eyes the swift onset of oblivion, and the abysses of eternity before us and behind; mark how hollow are the echoes of applause, how fickle and undiscerning the judgments of professed admirers, and how puny the arena of human fame. For the entire earth is but a point, and the place of our own habitation but a minute corner in it; and how many are therein who will praise you, and what sort of men are they?"