The reasons for the stock crash are as follows:

1) In the short term, it is caused by the relationship between supply and demand of stocks. If there is more supply, the demand will drop.

2) Long-term performance is determined by the company's performance. Poor performance will affect the price and make it fall.

3) Policies can affect people's expectations of the macro-economy and the company's prospects.

4) There are some peripheral factors, such as the financial crisis.