Managers buy and short at the same time, so that the portfolio will be less affected by emergencies, and its profit source depends entirely on the ability of stock selection. The whole strategy focuses on finding α value with potential profit opportunities, and then eliminating β value of market risk.
When the price of some stocks in the market changes, the range and time of the change are different. Fund managers take advantage of this difference to make profits. Use both bulls and bears to reduce market risk. A typical investment strategy is to choose a stock portfolio with a quantitative model, and then make half of the funds long and half short. For example, choose the strongest company and the weakest company in several industries. Put half of the funds in the stocks of the strongest companies to be long, and the other half in the weak companies to be short, or in index futures to be short.