I found the learned helplessness phenomenon very interesting. Learned helplessness is basically when an animal or human makes no effort to help themselves due to a lack of control over situations in the past; they basically give-up. It was first found in an experiment with dogs (Seligman and Maier, 1976) but it applies to humans as well. Learned helplessness is a characteristic of many depressed patients and it is also salient in education. Here's an example of learned helplessness in the classroom.
The book says that people most vulnerable to learned helplessness are people who suffer a series of unfortunate events such as losing a job, becoming ill, or getting divorced. Research also suggests that learned helplessness is less likely to occur for individuals who have successfully overcome misfortunes in their past. If you're curious how "in-control" or "helpless" you think you are, you can take a free, quick, and easy test here: mindtools: are you in control?