There is no way to be sure that the foundation will not go up. It should be analyzed from many aspects. Generally speaking, there are many reasons for the decline of funds, such as overvaluation of funds, frequent replacement of fund managers, and poor market conditions of funds.
If the fund market is not good, the whole sector is falling, but the fund's past income is not bad, and investors are still optimistic about the future prospects of this fund, then you can appropriately lighten your position and leave some funds to wait and see, and wait for the fund market to rise to make money, or there is a possibility of returning to the capital.
If the rate of return of the fund itself is poor, and the fund manager is frequently changed, and the position with relatively high valuation has been in a state of decline, then you can consider timely stop-loss redemption, and the possibility of returning to the capital is relatively small.
However, due to the large fluctuation of the fund, it is impossible to accurately judge whether it will rise or fall after the plunge. Therefore, if investors are optimistic about the future prospects of the fund, they can adopt the method of fixed investment of the fund to spread risks. If you are not optimistic, you can choose to leave some funds on the sidelines or redeem the stop loss in full.
Summary: There is no way to determine whether the fund will rise after the plunge. We should analyze it from many aspects. If the fund market situation is not good, the whole sector is falling, but the fund's past income is not bad, and investors are still optimistic about the future prospects of this fund, so they can appropriately lighten their positions and have the possibility of returning to the capital. If the fund's own rate of return is poor and the fund manager is constantly changing, then you can consider timely stop-loss redemption and return to the capital.