I know people (I am sure you do to) that eat, breath, and sleep their jobs.
If they aren't talking about work, thinking about work, making notes on what to do when next they are in the office, working every weekend, logging in and sending emails at midnight,... they aren't happy. They relish being bombarded with projects, with deadlines, with...
Ugh. It drives me nuts. It seems so un-rewarding. I know, I know, each to his (or her) own, so it must be rewarding some how. But where is the fun?
This life/work style is to be contrasted with those that work to live.