I was introduced to learned helplessness in my psychology studies many years ago, and it's one of several concepts that made a deep impression on me. To sum it up simply, animals and humans exposed to situations where they have (or don't think they have) control eventually act helpless, even at times when they can restore control. In short, people and animals can be exposed to experiences that make them act and be helpless even when things change.
This is an incredibly important psychological finding because it's a reminder of how experiences – and approach to handling them – affects our ability to take control of our lives and deal with stress. Many is the time I've witnessed people in the throws of learned helplessness, and I'm sure upon reflection you've seen it too. In fact, chances are you've experienced it now and then yourself.
I also see it a lot in people's careers, especially in this economic climate. I would go as far to say that I think learned helplessness is making the Great Recession far worse for many people.