It could be understood in this way. The earth was one's body, while the wood was fat. When wood grew from the earth, it meant that fatty meat was growing on one's body. This meant that one was fat.
If one used the wood that was grown below the earth, which was the wood that had grown in the opposite direction, wouldn't it mean that it would cause the reverse growth of fatty meat. This was equivalent to getting rid of the fatty meat.
Then, one had to look at the Yin and the Yang. The essence of the world was the Yin and the Yang. As long as one was in this world, this was the Great Dao. In other words, any object that survived among the laws of nature had two sides, Yin and Yang.
Earth that was found underground was Yin earth, which was the opposite of the Yang. Meanwhile, wood that was found in Yin earth was definitely Yin wood. The water that came from Yin wood was Yin water. The three Yin elements gathered.
