Happiness Isn't the Right Metric
At dinner the other night a colleague implied that money is rarely the reason people leave jobs–if they were happier at their current job, they wouldn't be looking around, or at least they would feel more satisfied with their current salary.
I agree that money is rarely the primary issue. And frankly it's always complicated as to why people leave (it's rarely one issue, no matter what the issue is). But I think we end up distracting ourselves if we look too rigidly to the "happiness" of employees. There's nothing wrong with happiness, of course, but there is a big difference between happy and engaged. Between happy and learning. Between happy and growing. Between happy and challenged.
If your constantly unhappy, then there's obviously a problem. But I don't expect to be happy all the time, and I expect other people I work with to have times when they are frustrated, when they struggle, or when the operating environment deals them a hand that is just plain hard. Loving your job is not about being happy all the time.