In 2010, Katrina Lake recruited 20 friends for an experiment: she wanted to see if she could choose clothes for them that accurately matched their style and personality. That idea sparked Stitch Fix, an online personal shopping service that aims to take the guesswork out of shopping. Today, it has over two million customers and brings in nearly a billion dollars in annual revenue. Plus, for our postscript "How You Built That", how Brian Sonia-Wallace built "Rent Poet" — a poem-on-demand service for weddings, corporate gatherings, and other events.