If enough players are in the market selling short, the phantom share issue mentioned about can mean that volume outstrips the actual number of shares outstanding. In a closely held company, for instance the actual float may be a small fraction of the total real shares.

Once one needs to cover there may simply be no available sellers from whom he can buy, particularly once a stock is coming off of its lows. And once he has been wiped out by a badly timed short sale, he may no longer have the cash to complete the transaction at a the market price once liquidity returns. Not sure I explained that well, but the fact is there is NOT always liquidity in ever single stock.

There were once stocks that were almost impossible to purchase at any price, simply because the shares were closely held by family or other parties whose interests were in managing or controlling the company, rather than simple speculation.