Why is there a ghost festival? Why do some people say that zero is the heaviest time in Yin Qi?

Because of the cultural background, the heaviest place in Yin Qi must be the Forbidden City, because it is the place where the emperor died and the place where eunuchs and maids died the most. Maybe it's the toilet, because the toilet is connected with the sewer, and the sun will never be seen in the sewer, which will inevitably accumulate Yin Qi, and it will only increase rather than decrease, so the shade will spread to the ground, not only the toilet, but also wherever there is a sewer.