What do you mean, don't use it in large-scale activities?

It means this day is not suitable for doing big things and making decisions.

First of all, people think that Red Sand Day is the third day in Meng Yue, the unitary day in the middle of the month, and the ugly day of the season and the month. That is to say, Shen Yin saw the fourth day of April, the first day of meridian and the ugly day in the morning. This is also what the almanac says.

Second, according to the theory of "turning to the gods", the red sand day is Meng You and Zhong Si, while the season is ugly. That is,1April 470 is unitary, 25881month is si, and March 369 12 is ugly. There is a saying: "Four Monks, Golden Rooster and Four Faithful Snakes, four seasons are ugly and red sand."

Extended data:

Four miles is considered as a day of seasonal change, and everything should adapt to the seasonal change. In the days when the four seasons alternate, people's behavior should follow the heaven, cultivate their own spirit, adjust their mood, keep their body and mind calm and static, and their spirit should be restrained and cannot release their essence. Therefore, it is recorded in ancient books that you can't have sex for four days (and four unique days), otherwise your life will be shortened by three years.

In addition, the traditional theory of choosing a date also thinks that the wedding day should avoid the four-mile (four-mile) day, because these days are in the transitional period of solar terms, and at this time the cosmic gas field is in a chaotic state and unstable, which is not conducive to marriage.