I’ve thought about this a lot as of late. Happy to throw in my $0.02:
I believe fulfillment to be an effect born from more powerful causes.
Chuang-Tzu’s statement of “Happiness is the absence of striving for happiness” rings true as it is very difficult to sit in a chair and actively strive to be fulfilled. It is a outcome derived, not pursued.
Instead, I believe pursuing endeavours that extend beyond ourselves is a righteous and ultimately fulfilling path. Most religions point towards loving our neighbours, and on a micro-scale, my anecdotal evidence guides me to believe service-oriented people/careers (teachers, firefighters) derive more fulfillment than ego-centric people/careers (financial services, sales).
I’d write fulfillment as a function of cultivating low expectations (the diminishing of ego), working in service for others, a thankfulness for our limitless blessings, and striving to bring change despite an impermanent life.
Or if shown through through the words of those wiser than I:
“Wealth consists not in having great possessions, but in having few wants.”
“The best way to find yourself is to lose yourself in the service of others.”
— Mahatma Gandhi
“Find something more important than you are, and dedicate your life to it.”
— Dan Dennett
“Gratitude is not only the greatest of the virtues, but the parent of all of the others.”
“That it will never come again, is what makes life so sweet.”
— Emily Dickinson
And most cogently:
f (fulfillment) = [expectation, service, gratitude, appreciation of time&death]