Jenn Hyman got the idea for Rent the Runway in 2008, after she watched her sister overspend on a new dress rather than wear an old one to a party. Jenn and her business partner built a web site where women could rent designer dresses for a fraction of the retail price. As the company grew, they dealt with problems that many female entrepreneurs face, including patronizing investors and sexual harassment. Despite these challenges, Rent The Runway now rents dresses to nearly six million women and has an annual revenue of $100 million. PLUS in our postscript "How You Built That," how Dustin Hogard and his business partner designed a survival belt that's full of tiny gadgets and thin enough to wear every day.