In yin-yang philosophy, it is explained that the north and the west are regarded as yin, the east and the south as yang, and that northeast and southwest become unstable because they are the boundaries between yin and yang.
陰陽道においては、北と西は陰、東と南は陽とされ、北東と南西は陰陽の境になるので、不安定になると説明される。