Why Do we question God?

Why when God instructs us to do something we question him? God is the creator, and we are his creation, so why question him? We question him, because we are not putting our full trust in him. We still waver in our faith, and think that God needs our help. God don't need our help he knows just what he's doing. Remember God's word says "Before you were formed in your mothers womb I knew thee". God knows all about us, so don't you think he knows what's best for us? Thoughts?