Technically, it is a short-selling mechanism.

The short selling mechanism is to borrow other people's stocks in advance, sell them when it is judged that the market is falling at a high level, and then buy them back at a low level and return them to the borrower to close the position for profit. Making a profit by rising is the opposite of buying stocks now. Because it makes a profit by falling, it will attract a lot of money to short in a bear market.

That is, you have a deadline, for example, you don't have any stocks on hand, but you short 1W shares (selling price 10 yuan/share).

On the maturity date, if the actual share price falls below 10 yuan, you can buy back 1W shares below the market price of 10 yuan (assuming 8 yuan per share).

In this way, the number of shares in your hand is zero, but you have an extra profit of 2W yuan.

However, if the real market price of the stock rises to 12, then you will lose 2W, because you have to buy back 1W shares at the price of 12 yuan per share in order to reverse your previous short position.