This important question has been pondered many times throughout church history. As a matter of fact, theologian John Calvin was dealing with the exact same question when he preached these wise words almost 500 years ago: "We must repeat the same supplications not twice or three times only, but as often as we have a need, a hundred and a thousand times. … We must never weary in waiting for God's help."
In other words, persistence in prayer is a good thing.
What Does God Say About This?
It's important, however, to realize we don't have to ask God for stuff because he's unaware of our needs. God knows everything about us. He knows every syllable we're going to pray before it even falls out of our mouth (Psalm 139:4). The simple reason we petition God is that he likes to be asked, perhaps because asking for his help is a declaration of our trust in his beneficent mercy.
Also, we don't have to pray over and over again to get God's attention or to twist his arm to act on our behalf; we get to talk to our Heavenly Father all the time and ask him for anything because he adores his children. Of course, we also have to rest in the fact that he knows best and his ways aren't always ours (Isaiah 55:9).
The following parable underscores the kind of parent-child communication we can enjoy with our Creator: "Then Jesus said to them, 'Suppose one of you went to your friend's house at midnight and said to him, "Friend, loan me three loaves of bread. A friend of mine has come into town to visit me, but I have nothing for him to eat." Your friend inside the house answers, "Don't bother me! The door is already locked, and my children and I are in bed. I cannot get up and give you anything." I tell you, if friendship is not enough to make him get up to give you the bread, your boldness will make him get up and give you whatever you need. So I tell you, ask, and God will give to you. Search, and you will find. Knock, and the door will open for you. Yes, everyone who asks will receive. The one who searches will find. And everyone who knocks will have the door opened. If your children ask for a fish, which of you would give them a snake instead? Or, if your children ask for an egg, would you give them a scorpion? Even though you are bad, you know how to give good things to your children. How much more your heavenly Father will give the Holy Spirit to those who ask him!'" (Luke 11:5-13, NCV).1