This question already has an answer here:
It's great to have a site where one can ask questions and get answers in a few hours, but what is precisely the motivition for them to do that? Are they altruistic? Or do they get money for it in the same way like one gets money for making video's on YouTube? I ask this because after getting an answer for questions, it feels 'fair' to give something back to the answerers if they are only altruistic.