when an investor is selling short and the market value of the underlying security has risen above the short selling price the proceeds from the earlier short sale would be less than what is needed to buy it back this would result in a losing position for the investor if the market value of the security continues to rise the investor would have to pay increasingly more to buy back the security if the investor does not expect the security to fall below the original short selling price in the near term they should consider covering the short position sooner than later 
example of buy to coversuppose a trader opens a short position in stock abc after their research they believe abc s stock price which is trading at 100 currently will fall in the coming months because the company s financials are signaling that the company is in distress to profit from their thesis the trader borrows 100 shares of abc from a broker and sells them in the open market at the current price of 100 subsequently abc s stock falls to 90 and the trader places a buy to cover order to buy abc s shares at the new price and return the 100 shares they borrowed back to the broker the trader must place the buy to cover order before a margin call the transaction nets the trader a profit of 1 000 10 000 sale price 9 000 purchase price 