The company’s sourcing narrative, the root of its brand identity, only adds to the business’s complexity. Sweetgreen is part of a small cohort of fast-casual restaurants, like Dig, Tender Greens and Mendocino Farms, for which supporting sustainable agriculture, and buying from small, local producers, is a core tenet. (It is by far the largest of this group, with the most funding.) To enter a new market, Sweetgreen sends a team almost a year in advance to build a roster of local farmers and artisans. That supply chain will not enjoy the same efficiencies as most any other fast food player. “If you’re McDonald’s, it’s easy to achieve economies of scale,” said Youngme Moon, a professor at Harvard Business School and a member of Sweetgreen’s board of directors. “When you’re trying to do something with local farmers, real food, fresh food, it’s a really different proposition. Is there a way to construct a business that’s able to grow and serve lots and lots of people, but is still able to hang on to the food-related values that made them start the business to begin with? That’s what they’re trying to unlock right now.”

And then there’s the question of demand. Tofu, trout and chicken hardly hold the same mass appeal as beef and pork, and Sweetgreen’s salads today cost around double the price of a Big Mac. That’s a winning formula in affluent urban locales, but how large, exactly, is the market for high-priced health food? Mr. Neman says that in the long term, automation might help lower prices to the level of Chipotle, which is about 10 percent cheaper, but he knows he’ll never be able to compete with McDonald’s on price. Developing items that are less costly to produce, which the company calls “menu engineering,” could also help Sweetgreen capture a different demographic. “How do we create a food that’s our Tesla Model 3?” he wondered.

Mr. Neman also believes that younger people will apportion more money to their health and, by association, healthy food. The rise of the $60 billion fast-casual sector, offering a fresher, healthier alternative to fast food for a premium price, suggests that such a shift is already well underway. Recently, he said, his research team turned up the insight that 50 percent of Sweetgreen’s customers had been to a McDonald’s in the previous 10 days. “It gets me excited about how big the opportunity is, and it reminds me how important convenience is,” he said.

Mr. Neman said he was inspired by Patagonia, the clothing company that promotes recycling and other environmental precepts. He’s also a great admirer of Disney, its vast library of content to suit all stages and ages, now piped straight to consumers with Disney Plus. I asked whether he admired any food brands.

Only Starbucks, Mr. Neman said, for expanding to more than 24,000 locations while staying quintessentially itself and continuing to evolve. Customer frequency, he observed, is the key to its business, and will be the key to Sweetgreen, too.