1. Institutions don't buy and sell with their own money like funds or insurance companies. Anyway, they are all investors' money, and they don't feel bad if they lose money. Moreover, management managers conduct underground transactions, and listed companies give red envelopes to fund managers, asking fund managers to buy company shares with investors' money at high points, thus raising stock prices or letting CEO of listed companies arbitrage their options.

2. Selling at the lowest point: institutions have previously shorted expired. If the physical stock is sold, the market index will go up and down, and the institution can buy the futures index at a cheaper price to settle.

3. Selling at the lowest point: the futures index is lower than the market index, and the institution buys the futures index, and at the same time throws out the real shares to hedge and earn the difference. This often happens in a bear market, that is, when the stock market is at a low point.

4. Buy at the highest point: the institution has bought the futures index before. If it buys real stocks, the market index will improve and rise, and the institution can sell the futures index at a higher price to settle the account.

5. Buying at the highest point: the futures index is larger than the market index, and the institution shorts the futures index, and at the same time buys the physical stock as a hedge to earn the difference. This often happens in a bull market, when the stock market is at a high point.