* I didn't think they would be this noisy (or messy or demanding)

* My allergies got too bad

* My bird attacks my boyfriend/girlfriend/husband/wife/children/dog/cat, etc.

* We had a baby

* We moved into a condo (or apartment, etc.) and can't keep him/her

* I work all day and he's lonely.  When I come home at night and need some time
    to myself he just screams at me for hours.

* He's starting to pluck his feathers (bite people, self mutilate, etc.)

Many people have unrealistic ideas about what owning a parrot will be like.  They see happy, well-adjusted parrots in zoos or gardens and they think this is what their parrot should be like, never realizing that these parrots are happy because they are interacting with people and other birds all day long.  Parrots are extremely social creatures.  They need companionship.  Often people buy a parrot, put it in a cage for 8 hours a day while they go to work and, after a while, the parrot develops serious behavioral problems.  This is not a good life for any animal, especially not one as intelligent and social as a parrot.