(be) careful what you wish for(, (because) you just might get it)

(be) careful what you wish for(, (because) you just might get it)

A warning that something that one desires might prove to problematic or undesirable were it to happen or come true. A: "I just wish they would give me a promotion with more responsibilities in work." B: "Be careful what you wish for. You might end up regretting how much more stressful your job becomes." A: "I don't know what to do with her—she's totally infatuated with Kevin and doesn't see what a jerk he can be." B: "Well, if they ever date, she'll figure it out. You know what they say—be careful what you wish for, you just might get it."
See also: careful, get, just, might, what, wish