A pyramid scheme is a model of business that is non-sustainable. Pyramid schemes should not be confused with legitimate multi-level marketing programs which actually provide products or services. They are illegal because it involves the exchange of money only to get others involved in the scheme without actually rendering any products or services. According to the U.S. Securities and Exchange Commission, they work by promising a lot of money to investors in a short amount of time. Pyramid schemes eventually get too big and collapse because of the lack of money the promoter is able to make to pay off investors.