I have been warned countless times by well-meaning folks that we need to be careful what we pray for because we just might get what we asked for. I understand the sentiment behind these words, but something about them has always kind of bothered me. However, it was only recently that I was able to articulate to myself what was eating at me, what had left me a bit uneasy. Actually, it took an episode of Nickelodeon's Fairly Odd Parents to bring my thoughts together. The storyline of the show was the difference in approach between a fairy and a genie. When you make a wish of a fairy, they pop up exactly what you had in mind. However, a genie is much more of a rogue. He grants your wish, but always with a twist or condition that you had not intended. For example, you wish for an omelet and it suddenly appears in your hands and scalds you. See, you should have wished for an omelet on a plate.
Thus the warning to be careful what you pray for seems to me to presume that God acts like some cosmic trickster. He will grant your wish, but He purposefully will answer it too literally or He intentionally will misunderstand you. You might pray for some quiet time and then are sentenced to 20 years in solitary confinement. You pray for a long life but get into an accident and live in a vegetative state for 30 years. I think this model of God as the ultimate trickster is one that we dare not take too seriously. I don't think of God as playing games like this. He is on our side and is always looking to meet us exactly where we are and take us to exactly where He wants us to be.
What is really behind the sentiment of being careful what you pray for really is a caution to be sure that when you pray you are certain that you want God to possibly intervene. If you pray for increased patience with people, don't be surprise if you find yourself in situations where you need to cultivate patience. In other words, you should approach prayer seriously with earnest intent. So, the sentiment about being careful what you pray for really is all about being sure that when you ask for help that you really want help.