In 1987, investors watched in horror as the Dow Jones Industrial Average plunged 22 percent in an event that became known as "Black Monday." Months later, the U.S. Securities and Exchange Commission published an 840-page report into the incident; in it was buried a seed that would eventually sprout into the $3 trillion market for exchange-traded funds. Eric Balchunas, ETF analyst for Bloomberg, has the story of the stock exchange executives who seized upon an idea to create what is now one of the world's most pervasive financial products - and the investors who passed them up.