What does 'Be careful what you wish for' mean?

If you get things that you desire, there may be unforeseen and unpleasant consequences.
('Be careful what you wish for, lest it come true.' and 'Be careful what you wish for; you may receive it.' are also used.)

All idioms have been editorially reviewed, and submitted idioms may have been edited for correctness and completeness.

See also: