This phenomenon only occurs in closed-end funds. Open-end funds, on the other hand, are not as affected by supply and demand because they are bought and sold at prevailing net asset values.
While a discount NAV could be an indication that the underlying assets in a fund will dip in value, it could also be a temporary market over-reaction. Moreover, the fund manager may decide to buy back shares of the fund to remove the discount and restore the fund's value back to its net asset value