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

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

First of all, it is considered that Red Sand Day is the third day in Meng Yue, the day in the middle of the month, and the ugly day of the season and the month. That is: Shen Yin sees the fourth day in the fourth month, the first day on the meridian, and the ugly day in the morning. This is also what the almanac says.

Second, according to "Turn to God", Red Sand Day is Meng You, Zhong Si and Ji Chou. That is,1April 470 is "unitary", 25881/month is "four", and March 369 12 is "ugly". There is a saying: "Four Monks, Golden Rooster and Four Bell Snakes, four seasons are ugly and red sand."

Extended data:

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

In addition, the traditional theory of choosing a date also holds that the wedding day should be avoided because these days are in the transition period of solar terms, when the cosmic gas field is in a chaotic state and unstable, which is not conducive to marriage.