Want to know what's really on an employee's mind? Ask them this: "What do you think about during your commute home each night?"
It is during this "decompression" time that most people think about their day, their life, their role. Are they making enough money? Working too hard? Appreciated enuff?
If they think about, "All the stuff I didn't get around to doing that day," that may be a sign of too-much work, or a need to evaluate their time management & prioritization skills. You may also want to check to see if they are making the appropriate amount of $$$, if you consider them a "keeper."
If they think about, "What's for dinner?" or, "Getting to the gym for my workout" then you've probably got a pretty happy employee.
If they think about, "Ideas to get more coverage for clients," then you've got yourself a winner.