The idiom “be careful what you wish for” is often used as a type of warning to people who are wishing for one thing, but might not realize all the negative consequences that could accompany obtaining that wish. Sometimes, the saying is followed by “it might come true,” “lest it come true,” “you may receive it,” “you just might get it,” or some other similar ending phrase. Due to the contradictory meaning of those two phrases, their combination might confuse those who have never heard the idiom in its entirety. Of course, whether the idiom provides a certain truth is entirely up to the situation. Often, the contradictory nature of the idiom does not negate the real warning it provides.
By itself, the saying might not have much meaning to those who have never heard it. Coupled with one of the other ending phrases, however, it becomes a rather oxymoronic or paradoxical statement. This means it contains elements that are seemingly contradictory. When a person tells another person to be careful about what he wishes for because his wish might come true, the receiver of the advice might think it is odd advice, given that he does want his wish to come true. In that sense, the phrase seems contradictory.
Like many idiomatic expressions, “be careful what you wish for” can be used in numerous everyday life situations. Usually, examples of appropriate times to use it combine a good outcome with a negative consequence. In other words, the person gets his wish, but it is accompanied by a negative result, too.
For example, a person’s neighbor might warn him to be careful about wishing to win the lottery, because of the money-related problems he could face upon winning. Likewise, a friend might warn another friend about wishing for a brand new car, because of the higher amount of insurance he will have to pay and the increase in risk of theft and vandalism his new car might face. One co-worker might warn another co-worker about wishing for a promotion, because of all the additional responsibilities that would cause personal stress and decrease the amount of time he can spend at home with his family. A homeowner might wish for a bigger house, without thinking of the increased utility bills that would follow. Each of these situations have both a positive outcome, meaning the person got his wish, and a negative consequence, meaning the person also received off-putting or even harmful results, as well.