When Katrina Lake applied to Harvard's MBA program, she wrote her application essay about an entrepreneurial aspiration she had: to create a business that applied data and recommendation algorithms to the retail shopping experience. During her second year of business school in late 2010, Lake began testing that idea by having friends fill out style-preference surveys and picking out clothes for them based on their answers. This one-person, low-budget operation would go on to become Stitch Fix, the mail subscription service that combines high-tech analytics and personal stylists to send women clothes they'll love.