To put it simply, for example, Zhang San and Li Si both sell eggs. At first, it was 5 yuan each, and then Wang Wu wanted to buy eggs, but he thought 5 yuan was too high and wanted to buy 4 yuan eggs. At this time, if no one except Wang Wu wants to go beyond 4 yuan, then Zhang San and Li Si will have to reduce their prices if they want to sell eggs. At this time, Li Si thought that 4 yuan was acceptable, so he made a deal with Wang Wu at the price of 4 yuan. Other people who want to buy eggs find that they can buy eggs for 4 yuan. Naturally, few people will go beyond 4 yuan, so Li Si has been selling eggs in 4 yuan. Then Zhang San and others found that such eggs could not be sold, so they all sold for 4 yuan, so the price of eggs dropped by 1 yuan.

Of course, there are also many cases of price reduction. For example, few people buy eggs, so Zhang San found that Li Si and 4 yuan were eager to sell them. When he gritted his teeth for 3 yuan, other wheat merchants followed suit, so that the price of eggs could be reduced even more. On the other hand, there are few eggs, and many people want to buy them, and they are snapped up for 5 pieces at once, so the seller raises the price, and only those who are willing to pay more can buy them. Anyway, there are so many eggs, and the price is gradually rising. This is a simple embodiment of "scarcity is precious"

This is just a simple explanation. In fact, the price is still affected by many factors. The following is an explanation as far as the market is concerned.