What you buy is an index fund, which determines the profit and loss according to the rise and fall of the stock. Each index fund corresponds to a corresponding stock index or stock concept. If the stock index or the corresponding concept goes up, the fund you buy will also go up, and if it goes down, the fund you buy will also go down. The net value of the fund is determined according to the rise and fall of the stock on the last opening day. The net value of the fund you saw today fell because the stock index or concept corresponding to the fund fell yesterday, and stocks generally fell yesterday. Today, stocks are mixed. If the stock corresponding to your fund goes up, the net value of your fund will go up tomorrow.