I think a lot about success, passion, and fulfillment at work. Here's a principle that ties all three together:

Everybody at the top of their game, from Warren Buffet on down to Jon Stewart, they all love what they do, and their love is what their makes their output so good.

I'm reading Warren Buffet's biography, and you see at an early age, he always loved numbers and collecting things. That, and he loved adhering to principles, like "Keep an Inner Scorecard." It seems that the reason why he's so successful is that he loves digging through financials personally, and he loves fighting all the powers that seek to push him away from a disciplined response.

Is it possible to succeed without loving your work? Absolutely. This is what happens to valedictorians, for example:

... few of the valedictorians seem destined for intellectual eminence or for creative work outside of familiar career paths. Dedicated to the well-rounded ideal to be a valedictorian, after all, you must excel in classes that don't interest you or are poorly taught; the valedictorians had used their strong work ethic to pursue multiple academic and extracurricular interests. None was obsessed with a single talent area to which he or she subordinated school and social involvement. This marks a difference, Arnold said, "from what we know about many eminent achievers, who tend to evince an early passion for a particular field." For these people, Arnold writes, "a powerful early interest evolves into lifelong, intensive, even obsessive involvement in the talent area." She goes on, "Exceptional adult achievers often recall formal schooling as a disliked distraction." Valedictorians, by contrast, conformed to the expectations of school and carefully chose careers that were likely to be socially and financially secure: "As a rule, valedictorians relegated their early interests to hobbies, second majors, or regretted dead ends. The serious athletes among the valedictorians never pursued sports occupations. Most of the high school musicians hung up their instruments during college.

(from An Interesting Statistic about Valedictorians)

Think of your favorite album or movie. Can you imagine the musician or director loathing it while making it? The most cherished products and successes you will almost always find, come from people who enjoyed doing it.

Could you imagine A-Rod hating baseball and being so good? Could you imagine Steve Jobs hating his job?