John Piper gives his thoughts on Matthew 7:9-11:
[W]hat man is there among you who, when his son asks for a loaf, will give him a stone?... If you then, being evil, know how to give good gifts to your children, how much more will your Father who is in heaven give what is good to those who ask Him!
One time when my son Ben was three or four, he asked for a cracker for snack time. I opened the box and found that they were moldy. I said, “I’m sorry, you can’t eat these. They are covered with fuzz.” He said, “I’ll eat the fuzz.” But I said no. He was not happy, but I loved him and would not give him a fuzzy cracker, no matter how much he pleaded.
So when Jesus says he will give good things, he means that. Only good things. And only he knows ultimately what is good for us. And notice, when he says dads don’t give stones when asked for bread, he does not say dads always give bread. Just no stones. And when he says, dads don’t give snakes for fish, he does not say dads always give fish. Just no snakes.
The point is this: God ignores no prayers from his children. And he gives us what we ask for, or something better (not necessarily easier), if we trust him.
Piper wrote his post to “overcome our skepticism” about our prayers being answered, and so motivate us to pray. But I see yet another application: We can trust that whatever the answer to our prayer is, no matter how it appears to us at the time, it is not a stone.