Why is there a mountain or a tall building behind the house to keep out the wind in Feng Shui?

According to the traditional geomantic theory, a "land of Shangji" should have a mountain in the north as the main mountain, and there is a mountain system behind the main mountain, the so-called "Long Mai", surrounded by a short mountain on the east and west sides, and a river on the south. Where the water winds around, the outlet and inlet of the water should have a good view. On the other side of the river, there should also be a distant mountain as a landscape, which is very close to the belt. This is the ideal feng shui pattern. First of all, the main mountain in the north blocks the cold wind in the north, and the two mountains in the east and west (Qinglong Shashan and Baihu Shashan) also make the site selection base less vulnerable to the cold wind. The water in the south brings moist air to the base, and the mountains facing south make it difficult for water vapor to disperse, so the north-south facing surface is the best direction for lighting, which is beneficial to the growth of plants and is naturally very suitable for people to live in. The ancients built cities, lived in settlements, and chose the natural geographical environment that conformed to the ideal feng shui pattern.