Finance and stock trading are so-called credit transactions. Financing is optimistic about the prospects for a stock that stock prices rise, people want to buy the stock, but the lack of cash, securities companies can borrow money to buy stock, the stock registered in the company's securities until after the stock rose entrust securities companies to sell , lending money with interest will be returned to securities firms, which earn the difference. Margin trading, compared with investors believe a stock will fall, when you want to take advantage of rallies to sell high-end, but not enough to suffer in the hands of shareholders, so the company a deposit of securities, borrow stock to sell. Cheap in buy back securities companies, which earn the difference.