It's the saying of mahjong feng shui. The main support of this statement is that the back against the window or door can be opened and closed, so it is virtual, while the back against the wall is real. Empty means leaking money, which is also the source of this statement.
Regarding the seat selection of mahjong geomantic omen, there is also a saying similar to "welcoming the door, losing the door" or homophonic "losing the bookcase".
It is very popular in mahjong circles to lose all the light by the window, which has something to do with Feng Shui. People who lean against the window will feel insecure in their hearts, which will affect their psychology when playing mahjong, and may lead to abnormal playing and more thorough loss.
Psychological function is the key, and feng shui is also one of the ways to strengthen psychological suggestion.
Feng Shui is a comprehensive and complicated science in ancient times, including environmentalism and humanistic psychology. The influence of the environment on a person is subtle, and the surrounding environment will unconsciously affect the mood.
Playing mahjong is the same. To put it bluntly, if you lean against the window, you will feel a little empty and insecure behind you. If there is some cool breeze outside the window, even if people's consciousness is not aware of it, their pores will be affected, and they will feel faint and uneasy in their hearts, which will affect people's concentration and normal mood.