This sentence is used to predict good and bad luck in Feng Shui metaphysics. You can understand it as: after going out for three to five miles, wearing black clothes can distinguish good and bad luck. Black clothes, China has always said that the sky is black and the earth is yellow. Xuan means black and the earth is yellow. Black represents the supreme and boundless sky. This unknown and profound sense of the universe formed Tianxuan's thoughts. Yin and yang refers to whether it is good or bad. The source is one of the auspicious days of the zodiac: There is no obstruction in going in and out, visiting the virtuous, traveling for three to five miles, wearing black clothes to distinguish yin and yang