Under Armour CEO’s three tips for growing a business by Patricia Sellers @FortuneMagazine April 28, 2014, 12:25 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons Under Armour founder and CEO Kevin Plank can’t stop competing. FORTUNE–“Our mission is simple: to make all athletes better,” says Under Armour founder and CEO Kevin Plank. “Our vision is even simpler: to empower athletes everywhere.” Have you noticed that the best businesses are typically built on easy-to-understand foundations? That is, one big idea. That was the message that Plank delivered last Friday in a keynote talk at a University of Virginia Entrepreneurs Symposium. Back in 1996, as Plank explained, he was a 23-year-old graduate of the University of Maryland, where he’d been special teams captain of the football team, and he was determined to invent a T-shirt that wouldn’t get soaked in sweat. Plank didn’t create the performance apparel category, but he made it mass-market, and that fielded lucrative opportunities for Nike and other companies that were smart and nimble enough to adapt. Meanwhile, he built a startup that generated $2.3 billion in revenue last year and has a stock-market valuation of more than $9 billion. UA stock is due to join the S&P this week. Plank, 41, had loads of advice for the entrepreneurs at UVa (my alma mater), but he said that his remarkable success comes down to three lessons: Focus. “We rebuilt that first T-shirt time and time again during the first five years,” Plank said about Under Armour’s early product development. “People kept saying, ‘You should do this…You should do that,’” he recalled, noting that he ignored advice to broaden his product line. Two decades later, Under Armour sells shoes and sunglasses and all sorts of athletic gear, but the original product, the moisture-wicking T-shirt, is still in development. “I think we’re on the 63rd version of that shirt,” Plank said as we chatted after his keynote. “It’s key to become ‘famous’ for one thing first,” he added, “and that will give you the credibility to go into other areas once your ready….which generally means a long time and a lot of perfecting!” Find out if your product can sell. Before he created Under Armour, Plank had an on-campus rose-selling business, Cupid’s Valentine. He invested $16,000 from that business into his T-shirt startup in 1996—and $9,000 of the $16,000 went into patents and trademarks. “Save yourself time and money,” Plank said, contending that he overspent on legal fees. Early on, use scarce capital to “get your product into stores,” he advised. Possess strong will. “I have a saying at the company,” Plank said as he described how he talks to his 7,000 employees’ about their Baltimore-based company’s culture of ownership. “Employees get things done. Partners get things done done. But owners get things done done done.” Listening to Plank, I thought of other leaders like him who created multi-billion-dollar businesses from one idea. Whole Foods founder-CEO John Mackey has done that. So has Hamdi Ulukaya, who created Chobani Greek yogurt and built a business that grew as fast as Google and Facebook in its first five years. Read Beth Kowitt’s exclusive Fortune interview with Ulukaya about his new $750 million investment from private equity firm TPG—and her Fortune cover story about Whole Foods. Meanwhile, brand expert Jim Stengel, the former CMO of Procter & Gamble , captures the essence of enduring growth companies in his six-part series here. Growth begins with a big idea, and if you’re smart and lucky, it never ends.