This past weekend, I was looking over a Meetup.com webpage for a group going to a new musical called Come From Away this Sunday night—the 15th anniversary of 9/11. The show focuses on the trans-Atlantic flights on that fateful day that had to be grounded in Gander, Newfoundland, and how the people of the town welcomed the passengers.

A quote from Marc Katz, who started Custom­Ink 16 years ago in the basement of someone's house—very SIPA-like for a beginning—struck me recently. Last year, the online T-shirt company piled up $300 million in sales. The question that most caught my eye in The Washington Post interview was this: "What's the basic business premise?"