Or which one of you, if his son asks him for bread, will give him a stone? Or if he asks for a fish, will give him a serpent? If you then, who are evil, know how to give good gifts to your children, how much more will your Father who is in heaven give good things to those who ask him!
We do not have to persuade God to be good to us. He is a loving Father who loves to give good gifts. Even as sinners, we care for and provide for our children so we can expect God to do that but in a perfect way that we could never achieve. So, if we think God is withholding something for us, it's likely to be for the same reasons you might withhold something from a child - when it is in their best interests. The child may be upset at the time, but the parent knows more about the bigger picture. God knows our needs better than we do and can be trusted.