Learned helplessness

In 1965, psychologists Mark Seligman and Steve Maier conducted an experiment in which three groups of dogs were placed in harnesses. Dogs from group one were released after a certain amount of time, with no harm done. Dogs from group two were paired up and leashed together, and one from each pair was given electrical shocks that could be ended by pressing a lever. Dogs from group three were also paired up and leashed together, one receiving shocks, but the shocks didn’t end when the lever was pressed. Shocks came randomly and seemed inevitable, which caused “learned helplessness,” the dogs assuming that nothing could be done about the shocks. The dogs in group three ended up displaying symptoms of clinical depression. Later, group three dogs were placed in a box with by themselves. They were again shocked, but they could easily end the shocks by jumping out of the box. These dogs simply “gave up,” again displaying learned helplessness.

http://en.wikipedia.org/wiki/Learned_helplessness