It made me wonder -- is it okay to pray about the same thing over and over again? Can you "over-pray"? God already knows our hearts. He already knows His will. Should we just ask once faithfully, or should we be persistent in our prayers?
Turning to Scripture is always the best way to get answers to questions like these. There are two parables in Luke that provided answers for me.
One Example is in Luke 11:5-13
Then He said to them, “Suppose one of you has a friend, and goes to him at midnight and says to him, ‘Friend, lend me three loaves; for a friend of mine has come to me from a journey, and I have nothing to set before him’; and from inside he answers and says, ‘Do not bother me; the door has already been shut and my children and I are in bed; I cannot get up and give you anything.’ I tell you, even though he will not get up and give him anything because he is his friend, yet because of his persistence he will get up and give him as much as he needs.
“So I say to you, ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you. For everyone who asks, receives; and he who seeks, finds; and to him who knocks, it will be opened. Now suppose one of you fathers is asked by his son for a fish; he will not give him a snake instead of a fish, will he? Or if he is asked for an egg, he will not give him a scorpion, will he? If you then, being evil, know how to give good gifts to your children, how much more will your heavenly Father give the Holy Spirit to those who ask Him?” (Luke 11:5-13 NASB)
Jesus is saying here that if you keep pounding on your friends door, he'll eventually get up and give you what you need. Not just because he is your friend, but because you've been persistent and wouldn't give up.
Another example is in Luke 18:1-8
Now He was telling them a parable to show that at all times they ought to pray and not to lose heart, saying, “In a certain city there was a judge who did not fear God and did not respect man. There was a widow in that city, and she kept coming to him, saying, ‘Give me legal protection from my opponent.’ For a while he was unwilling; but afterward he said to himself, ‘Even though I do not fear God nor respect man, yet because this widow bothers me, I will give her legal protection, otherwise by continually coming she will wear me out.’” And the Lord said, “Hear what the unrighteous judge said; now, will not God bring about justice for His elect who cry to Him day and night, and will He delay long over them? I tell you that He will bring about justice for them quickly. However, when the Son of Man comes, will He find faith on the earth?” (Luke 18:1-8 NASB)
This judge wasn't a nice guy. He isn't compassionate toward those who come into his court. For many days he had put up with this lady. She seems to be brave in a time when women didn't have many rights. She keeps persevering until finally the judge gives in. She wore him down.
Don't think of these two parables in the sense that God would be the annoyed friend or the mean judge. Think of these as models for prayer. Keep knocking on your friends door and keep pestering the judge. Keep asking God for what is in your heart and what occupies your mind. If something is lingering in your heart beyond one fleeting moment, perhaps it's worth asking for. Pray as long as you need to because God understands -- he already knows your heart.
I know for me, as I've continued to pray, I've gained a better understanding of what I'm praying for. I've become more confident and like the widow, more courageous.
God already knows what we need and and He knows what we want. He wants us to be content. He will never ask us to glorify Him in any way for which He will not supply us.
But seek first the kingdom of God and His righteousness, and all these things will be provided for you. Therefore don’t worry about tomorrow, because tomorrow will worry about itself. Each day has enough trouble of its own. (Matthew 6:33-34 HCSB)