The first place where quantum gravity is needed is near the center of black holes. It is believed that quantization of gravity is necessary to solve the singularity problem. The same is true of the early days of the universe. The universe is not static; it is thought to have been expanding ever since its birth. In other words, if we go back in time, it is inferred that the universe was in a high energy and high density state, and it is thought that we eventually reach a region where quantum gravity is required. Here, we reveal the causes of the various problems that occur in these regions and argue that quantization of gravity is necessary to overcome them.