Ладно, я напишу.
It is a very interesting question. The primary requirement is satisfaction. But that's not so simple, as you should suppose at this place. For one sort of people, everything is counted in terms of money. For them, it is the money and only the money what makes the world go round'n'round. For others, the primary requirement is to get fun from job, to like it.
Jobs are different, yeah. Very different. Just compare a job of elementary school teacher with a job of president of company. President lives in absolutely another internal (and somehow external too) world than school teacher.