As a sister to my comment I'll also add you can effectively (though not legally) short more stock than you can buy. This is because to short you pay for a stock at the current market price with the promise to sell it back at the same price to the lender at a future date. If you then immediately sell the stock you can use that money to immediately pay to borrow another stock.

This means with the cash it takes to buy 1 share you can short as many shares as someone will lend which can multiply your loss to more than you have.