Seligman Theory influenced on psychologist research of depression in the 1970s. he accidentally discovered helplessness when he was studying the effects of inescapable shock in dogs. he restrained dogs in a Pavlovian harness and administered several shocks paired with conditioned stimulus just like classical conditioning. Later they were placed in a shuttle-box where they could avoid shock by jumping over a barrier. This was also used in the operant conditioning learning. The experiment have problems because most of the dogs failed to learned how to avoid the shocks they were receiving.