They say, “Be careful what you wish for”, and they’re right.
Example One:
Everyone always wishes for a white Christmas. Then, when it snows at Christmas time, everyone gets all miserable and angry because they can’t travel and they keep falling over when they venture outside.
Be careful what you wish for.

"No sign of Cipriani..."
Example Two:
On the piece of televisual brilliance that is ITV’s Take Me Out, if the man isn’t a 54-year-old total fruitloop living with his parents and collecting human hands, he’s usually left with the choice of several women at the end. He quickly whittles these down to just two, using a process of: face like a bag of smashed crabs – out, probable ‘tard – out, slightly slutty – in, 6’5” and 16 stone – out, and so forth, until he’s left with just two potential partners. Often, one of these is a bit more attractive than the other. That’s just the way life works, right. They’ll each say a little something, and you can bet your last smashed crab that the less attractive one will say something much nicer than her more aesthetically pleasing rival. At this point, you can almost see the conundrum running across the bloke’s eyes. Without fail, literally EVERY SINGLE TIME, he’ll pick the prettier, more of a twat one. And it will end in misery.
Be careful what you wish for.

"What's that, he's hiding under my dress?"
Example Three:
We like Kelly Brook. A lot. So much so that we want her to be happy more than almost anything. Or rather, we wanted her to be happy. Even at the expense of our own happiness. Or so we thought. But now she appears to be back with this Danny Cipriani fella, we take it all back. We don’t want K-Bro to be miserable, that’s for sure, but we don’t want broken hearts, which is what seems to be happening at the moment. Why is she back with him? How can this be happening? We’re STILL available y’know, Brookster. We’ll come to a lovely little remote island with you, if you want. We'll watch Love Actually with you and play in the snow and won't even get angry when you get us right in the eye with a snowball that contains a bit too much ice to be safe. We'll even let you have some of the good cheese.
Be careful what you wish for.

"There he is!"