Some brief thoughts on some of the typical motivating factors behind my behavior...
HAPPINESS: The big one. I like being happy - I do things that make me happy, which in my case means plenty of geeky things like cartoons and video games and toys and such. However, I also like making other people happy, especially people I care about - it's just about the only thing I've exer experienced that gives me any real sense of accomplishment/satisfaction/pride. I do something for myself? Eh, no biggie. I do something nice for someone I know and she gets a huge grin on her face and gives me a big hug? I feel like the most special guy in the world.
As an extension of this, I dislike seeing people I know unhappy, and I absolutely *despise* mean people - those who would cause *un*happiness out of some warped sense of sadism. Which leads us to...
VENGEANCE: I am a strong believer in the concept of karma - that good things should happen to good people, and that bad things should happen to bad people. I am vengeful; if someone wrongs me or a friend of mine, I want them to suffer an appropriate karmic payback. With any luck, it will get them to reconsider their behavior...or, failing that, it will at least discourage them from being assholes out of fear of karmic reprisal.
JUSTICE: Everybody gets treated fairly - no exceptions. If I *do* feel the need to retaliate against someone, it's always done in measure with their own behavior. I forgive easily, but only if I feel the person is being sincere in their apology and is genuinely sorry. I give everyone a fair chance - if a plain-looking girl asks me out on a date, and then a much cuter girl asks me out on the same night, I'm going to turn her down so that the plain girl has her fair chance to win me over.
NECESSITY: Some stuff just *needs* to be done - keystone actions, without which everything else falls apart. I work because I need money to survive. I don't *dislike* my job, but I don't get any sense of great enjoyment out of it either - if I win the lottery and get rich some day, the first thing I'll do is quit my job and never work another day in my life.

I *hate* washing dishes, dusting, taking out the trash, etc., but if these things don't get done then I end up wallowing in filth, so I grit my teeth and get them over with. Grim determination.
You know how people take up running because of Emi? Yeah...I don't do that. But what I did instead is consider how I've neglected taking care of my body in that physical regard, do a careful lookup of how I could stay fit in ways that are much more personally acceptable to me - and then I kept doing it regularly for the past 2 months, never missing a term so far. And it works. So I don't try to imitate Emi by running every day. Instead I take care of my body in my own way, because Emi reminded me that it's an important part of my life.
Heh. I wound up the same way, sort of. I initially started out trying to exercise, under the impression that my couch potato lifestyle would make it difficult-to-impossible for me to lose weight and that the next best thing would be to increase my physical strength and cardio to better compensate for being a fatass.

But then, after reading a fitness book and learning a lot of good info on healthy, effective dieting, I tried that instead - and to my shock, it seems to be working. I've stopped with the intensive exercise for now and am instead focusing on maintaining my diet; my plan is to lose as much weight as I can before I start back with the workouts, since the more weight I lose, the easier it will be to work out without overexerting myself.