Since ancient times, mirrors have attracted close attention of people. They are believed to have great magical powers. So, there is an opinion that you cannot look in the mirror at night.
The Slavs believed that through mirrors they are portals in the world of the dead, and therefore otherworldly forces can penetrate through them into the world of people. That is why, on the day of the funeral, all reflective surfaces in the house are still covered with dark matter.
From the beliefs of many peoples, one can learn that mirrors do not just reflect real things, but preserve the reflected images, absorb energy. The older the mirror, the more it sees events. And if something bad happened in front of him, then he can remember this, and therefore it is considered even more dangerous.
So why can't you look in the mirror at night? The Slavs believed that if you look at your reflection in the dark, you can see evil spirits that are on the other side of the glass. They are fueled by the energy of the beholder and can come out from the other world.
On Christmastide days, Slavic girls usually used to guess at their betrothed, while mirrors and candles were often used for this. Such methods were used only by the most desperate girls, because due to superstition, most were afraid to resort to such methods to see their fate. It was believed that at this time in the mirror in the dark by the light of candles one could see not only the future, but also the devil himself. At the same time, you can be so scared of what you see that at best you become a stutterer, and at worst - even get sick with a serious illness and die.
When asked why you can't look in the mirror at night, it should be noted that most of these fears are prejudices that should be treated with humor. After all, if you believe in every omen and superstition, then you can actually bring trouble on yourself, because, as you know, thoughts are material.