When you short sell a stock, you are borrowing the stock from a lender, and the lender always has a right to say that they need their shares back, which might result in a forced buy-in by your broker. According to this site, buy-ins are very rare, and almost never happen.
But wouldn't it make sense that if a certain stock started plummeting (because of some negative company event, etc.), most of the lenders of that stock would want to sell their positions right away, to avoid losing even more money? If so, then forced buy-ins should happen alot more frequently - every time some stock sharply nosedives... How come that is not the case?