Suffering is, because happiness is. Suffering and happiness are interdependent co-arising. Happiness must have manifested at the same time if suffering has manifested. Maybe we can find happiness if we see from behind. Suffering is like a pain which tells us something is wrong with our body. Suffering is telling us that something is wrong with our mind. The ultimate truth in the phenomenal world is that suffering is no other than happiness. Suffering and happiness are two sides of the same coin. And the ultimate truth in the noumenal world is that there is no suffering.