I'm a Christian, so let me try to answer this.
"The heart knows its own bitterness, and a stranger does not share its joy." - Proverbs 14:10
All relationships are dependent on faith. After all, we can never fully understand another person, so some degree of trust is a requirement. I see no difference between trusting God to answer my prayers and trusting my wife not to cheat on me.
If we cannot know our finite fellow human beings fully, how can we be expected to know God? Only after we have died and gone to heaven can we even begin to truly comprehend Him.
During the Exodus, God repeatedly aided the Israelites. And yet, for all these demonstrations of His love, guidance, and power, they still betrayed Him, first by worshipping a gold calf, then by refusing to trust Him to keep them safe from the Canaanites.
The Bible also speaks of a time when Jesus will rule the Earth from Jerusalem for 1,000 years. He will rule with great justice and righteousness, yet at the end of the millennium, Satan will have no trouble raising an army in rebellion against Christ's rule. The problem is not with God, but with humanity.