There's a study done on dogs where the dogs are in kennels and food is placed outside a door -- but any time a dog sticks its head through the door, they get an electric shock. Some dogs just need to be shocked once to back away; other dogs try numerous times, but in the end, all dogs choose starvation over the physical pain they know is going to come if they try to get to the food.
And after a while, the electricity is turned off, and the dogs will still choose to starve rather than risk the pain.
Once conditioned to learned helplessness, the dogs will bite anyone trying to get them through the door to the food. They need to be put on a leash and basically pulled through the door by the leash. Some dogs get it the first time and go, "Hey! Wow! Look! No pain! Awesome!" and after that walk out to eat. Other dogs have to be pulled through 10 times. 20. 30.
But the good part is that all dogs eventually un-learned the helpless behavior. It just took some longer than others.