Because the good news of a company has come out before it comes out, the news is in a hazy state, when the stock price rises with the participation of investors. By the time the news really came out, the stock had gone up a lot. At this time, profitable investors want to take profits, and then the stock will fall. Of course, there are investors who continue to rise. In this case, more investors continue to buy rather than sell. As a result, a lot of news officially came out and the stock began to fall.