The ancients discovered during the process of physical fitness and self-cultivation that there are signs of water and fire in the human body. However, if the water and fire in the human body do not complement each other, they will fall ill.
The ancients believed that the human body's kidneys accept the image of water, and water should rise; while the heart accepts the image of fire, and fire should decrease. This is the combination of water and fire.
"Jiji" comes from the "Book of Changes" and is the 63rd hexagram in the "Book of Changes". The "Jiji Gua" has the upper ridge and the lower level, so it is called "Water and Fire Jiji". Kan is water, and Li is fire. If it is Ji, water and fire intersect for use. The saying "water and fire are both harmonious" in traditional Chinese medicine refers to the mutual support and mutual restraint in the Five Elements theory to describe the relationship between heart fire and kidney water.
The heart fire descends to warm and nourish the kidney water, and the kidney water rises to extinguish the heart fire. When the heart and kidneys intersect, yin and yang are harmonious, and the body is healthy, it is called "water and fire are combined"