I have met a large number of people who love their jobs and have burned out. I'm not really sure that anecdotal evidence is going to satisfy people in this thread of the conversation, so I suspect my volunteering of this is of little utility.
Maybe another way to look at it is the "burn out rate". Different companies have a tendency to turn excited new tech employees into minimally-productive ones in different time frames.
For example Amazon has a burn out rate of about a year, whereas Google and Facebook are about two years and Microsoft four years.
Why should this be the case? I think people above in the thread would argue that it has to do with culture and working conditions, with moral and with levels of individual autonomy.