Senior correspondent Michael Arndt asks Steve Ells: What is the one thing you're happiest you did when you opened your first Chipotle Mexican Grill 11 years ago?"I followed my instinct. People told me I was doing a lot of things wrong -- the size of the burrito, the spiciness, the open kitchen, the price point, the limited menu. But those things make Chipotle successful today. We're not a brand that developed from focus groups." -- STEVE ELLS, founder and chief executive of Chipotle Mexican Grill, now a 360-store unit of McDonald's Corp.