It's sunny in spring and summer, warm in spring and cool in summer. The sun shines in spring, and the evil of wind and cold is still a problem. In spring, we should pay attention to keeping warm and keeping out the cold. According to a folk proverb, clothes should not be cut down prematurely in spring, that is, the sun of human body should be kept well. In summer, the sun is extremely strong, heat is evil, heat consumes gas, and gas is also yang, so heat also hurts the yang of human body. In summer nights, people like to enjoy the cool, and are vulnerable to the evil of cold and dampness, thus hurting the yang. It's hot in summer, people like cold drinks, and eating too much is easy to hurt the sun. Therefore, in summer, we should not only enjoy the cool and escape the heat, but also avoid drinking cold drinks so as not to hurt the sun; When enjoying the cool in summer night, avoid wet dew and cover it properly to avoid wet and cold.

Cloudy in autumn and winter, cloudy in autumn and cloudy in winter. In autumn and winter, dryness and evil can damage yin, so taking nourishing yin or applying moisturizing skin care products in autumn and winter can also help prevent dryness and keep indoor air moist. It gets colder in autumn and colder in winter. People like to eat spicy food and drink to keep out the cold. Spicy products are easy to get angry, wine is easy to get hot and humid, and eating too much hurts yin. Therefore, it is necessary to avoid dryness and evil in autumn and winter, and avoid overeating to prevent yin injury.

People think that summer is warm and evil, and summer is easy to hurt yin, so it is necessary to nourish yin in spring and summer; Cold evil in autumn and cold evil in winter are easy to hurt yang, so it is necessary to raise yang in autumn and winter. Why does Neijing only emphasize "nourishing yang in spring and summer and nourishing yin in autumn and winter"? As we all know, warm spring and summer are easy to hurt yin, and cool autumn and cold winter are easy to hurt yang. In spring and summer, people know how to raise yin but not Yang. In autumn and winter, people know how to raise yang but not Yin. Therefore, in spring and summer, there are people who seek to nourish yin but hurt yang; In autumn and winter, there are still people who hurt yin because they want to raise yang.

Neijing is ignored by many people in the world, but saints who are good at keeping in good health can know it. Therefore, it is said that "saints nourish yang in spring and summer and yin in autumn and winter" obey the changes of yin and yang in the four seasons, that is, "follow their roots".