What causes a bird to take it's unhappiness out in such an extreme manner is cause for speculation. There is no doubt that abuse, neglect, and lack of attention cause behavior problems such as screaming, biting, and feather mutilating. I also believe that lack of early socialization, lack of exposure to change during weaning and infancy, and lack of consistency in setting firm guidelines can contribute to a birds inability to cope with stress and change in a positive manner. It is critical that hand-rearing and weaning be preformed by experienced aviculturists. Experienced breeders should mentor beginners under their direct supervision to ensure proper education and training.
Prevention is the key.
There are different forms of feather mutilation which vary in magnitude from bird to bird. Feather plucking is when the birds completely remove the feather by pulling it out at the base of the shaft. Some birds will chew the feathers off a little bit at a time, never completely removing the feather. Repeated feather mutilation over a period of time can cause permanent follicle damage, thus preventing these feathers from ever returning. In severe cases the birds will self-mutilate soft tissue areas on their breasts, legs,and backs causing sores and bleeding.