An interesting question

My previous post poses an interesting question. I often wonder why some people so easily settle for things while some are always seeking more. Example. I work a 9 to 5 job, 40 hours a week, and I'll be the first to admit that I'm not totally content with that situation. But others who I work with, who do very similar tasks, love the job and you can sit it in dealing with them on a daily basis. They are the ones who make the office a fun (relatively) place to work, and I'm certainly not mocking them for doing so. They are truly the ones who make working somewhat enjoyable. But sometimes it seems to me that they enjoy it too much. Do they not see that they are just a cog in the big wheel? Or maybe they do see it and that is ok. Maybe I'm the one missing something.

What makes certain people content to be on call for someone else, working day in and day out without thinking twice? And why are others so discontent with the same situation?