From Manual of Parrot Behavior edited by Andrew Luescher (a textbook for veterinary students):
"From a behavioral perspective, hand-rearing reliably produces tame, human-habituated birds that tend to talk more than do parent-reared birds.
However, hand-rearing may also be at the root of a number of behavior problems in companion parrots. Hand-rearing alters Orange-winged Amazons’ social preferences and sexual behavior and may lead to hand-reared parrots inappropriately directing sexual behavior (both courtship behavior and aggression) toward humans. Anecdotally, sexual aggression directed at humans is common in a number of parrot species, especially in male amazon parrots and male cockatoos. Similarly, parrot owners often report that their parrots regurgitate for them or attempt to masturbate against their owners’ hands or bodies. Although a strong social preference for humans may be endearing in a parrot chick, sexual aggression and inappropriate sexual behavior can be problematic in older birds. Hand-rearing may also be related to the “phobic” behavior that has been described in pet parrots. In the lay literature, phobic behavior is defined as a behavior pattern in which “a previously tame and affectionate parrot ‘suddenly’ seems afraid of almost everything and everyone” This sudden, apparently inexplicable, fearfulness usually appears in hand-reared birds around the age at which they would typically become independent of their parents in the wild. “Phobic” or anxious parrots often injure themselves trying to avoid aversive stimuli, often breaking blood feathers and injuring their keels in repeated falls (Clark 2001). Obviously, the sudden appearance of such extreme and apparently unexplainable fearful behavior in a previously fearless bird can be disconcerting and would certainly appear pathological. Hand-reared parrot chicks are endearing, oftentalkative, and fearless. However, this period of outgoing fearlessness is only temporary. By one year of age, hand-reared and parent-reared Orange-winged Amazons behave identically inresponse to a novel object, suggesting that the period in which hand-reared birds appear particularly well adapted to captivity may only be temporary. "