Why God?

This is a very common question. So common a lot of sermons have been preached on this subject. Many books have been written in this subject. I suspect many journals have been consumed by this subject. But my "why" question is different. My "why" question is why do we complain? Myself included. God is so faithful, so good, so merciful. He has proven Himself over and over again. Why do we not get it? Why do we not trust the ever knowing God? He knows us better than we do. He knows the future, we don't. He keeps His promises. He never lets us down. So again, why do we complain against God?