They learn that mutual preening comes from a human's hand, rather than another parrot's beak. They learn that family pets, such as dogs and cats, are to be chased and tormented, rather than avoided as predators. They see their humans as their friends and fellow members, because after all, those are the ones who gave these baby birds their meals and warmth. Unfortunately, this utopia of bird to human relationship has one flawed edge. Our African Greys are still very much wild animals.
Instinct is the species' way to insure their future existence.
For instance, parrots are prey animals. They are eaten by predators who are the parrots' natural enemies. While we can change their learned behaviors through imprinting, we cannot do anything toward changing responses and behavior patterning in these parrots that are so many generations away from being domesticated. Domesticated animals, such as dogs, have had many of their genetic behavior traits bred right out of them, leaving them all the more susceptible toward complete imprinting on their human caretakers. When a parrot cannot cope with an event, it falls back on its instinctive responses.