God knows how to give good gifts to His children, just as fathers do. But fathers know not every "good gift" is thought "good" by children.
It's not all peaches and ice cream: sometimes God gives us vegetables and hard chores.
"Building character" isn't always the same as how we define prosperity. And God's "good things" for others may result in some discomfort or pain for us (short-term, at least in the light of eternity).