Peter Lynch wants you to know that his ideas are being misquoted widely.

“I’ve never said, ‘If you go to a mall, see a Starbucks and say it’s good coffee, you should call Fidelity brokerage and buy the stock,’ ” Mr. Lynch says, some 25 years after his retirement from running Magellan Fund was front-page news.

Following the market still at age 71, he instead explains his philosophy this way: Use your specialized knowledge to home in on stocks you can analyze, study them and then decide if they’re worth owning. The best way to invest is to look at companies competing in the field where you work. Someone with deep restaurant-industry experience would have predicted the success of Panera Bread Co. and Chipotle Mexican Grill Inc., he says: “If you’re in the steel industry and it ever turns around, you’ll see it before I do.”

What’s wrong with the popular-wisdom version of his ideology, which is usually cited as “invest in what you know”? It leaves out the role of serious fundamental stock research. “People buy a stock and they know nothing about it,” he says. “That’s gambling and it’s not good.”

Mr. Lynch was a mutual-fund rock star. When he ran Magellan, he says, one of every 100 Americans was invested in it. Though he is on boards at Fidelity Investments in Boston, since leaving fund management he has kept to philanthropy. With his late wife, Carolyn, who died in October, he ran a foundation that funded mainly educational and health-related nonprofits in Massachusetts and beyond, such as Teach for America, Partners in Health and the Posse Foundation. He managed the money and Mrs. Lynch chose the recipients.