This sentence comes from Jay Chou's song Blue and White Porcelain, "It's raining in Lan Yu, but I'm waiting for you". Due to the limitation of ancient science and technology, the ancients could not change the humidity. "Azure rain" is the top grade of blue and white porcelain, and it is a very difficult color to make. There are only a few hundred in the world. When burning in the furnace, the moment it comes out must be rainy, and craftsmen need to wait until the temperature and humidity in the rainy season. The end result is that Blue can't wait for misty rain, and I can't wait for you.