When tragedy strikes, we ask God, "why"? Our human limitations do not allow us to see the full picture or plan. Questions are expected when there is uncertainty or unknown situations that arise. God expects the questions, but He also expects us to trust Him.
Hebrews 11:6 (Living Bible) says, "You can never please God without faith, without depending on him. Anyone who wants to come to God must believe that there is a God and that he rewards those who sincerely look for him."
It is ok to ask why. He expects it. However, when we ask, we must not only believe IN God we must believe God and what He says.