Well, from what I know from my friends (They are the ones you are asking about), its just competition with other players. Its that need to be the best out of the people you know, plus, they have absolutely no lives. All their friends are in the game or online 90% of the time, they have no significant others, and they have nothing but free time. I've tended to grind for a day or so but the only thing keeping me sane from it was that I was talking to my friends on the phone or AIM or be at their house.
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