Between 1977 and 1990, when he suddenly retired at age 46, Peter Lynch grew Fidelity Investments’s Magellan fund from a $20 million pipsqueak into a $14 billion giant and became a Wall Street legend in the process.

In a 1989 Fortune article titled “Secrets of a Champion Investor,” a young Andrew Serwer, now editor-at-large of Barron’s, spoke to Lynch about his investing philosophy in a lengthy interview. The takeaway for retail investors was rather simple: Look for thriving businesses at “cut-rate prices,” and do your homework to understand the firms’ operations fully before investing.

Lynch described how he would spot quality companies in the real world, by sampling a Taco Bell burrito or noticing that his wife preferred Hanes brand panty hose; then analyzing their growth prospects, business model, balance sheet, valuation, and even “kicking the tires” at the firm—making in-person visits and calls to employees—before making an investment. This “buy what you know” style, which Lynch later detailed in his 2000 book called One Up on Wall Street, helped the money manager outperform his peers for decades, and has garnered him an audience among retail investors seeking prudent advice during retirement.

But even the best investors make mistakes, and for Lynch, his most glaring errors are the opportunities that got away. In a April 25 CNBC interview, he described missing out on the rise of Apple and the chipmaker Nvidia, despite seeing signs of the success of their businesses in the real world years ago, just as he once had with Taco Bell and Hanes decades before.

“Apple was not that hard to understand. I mean, how dumb was I?” Lynch, who now serves as vice chairman of Fidelity Management & Research, lamented, describing how he noticed his daughter buying an iPod in the early 2000s and found out Apple was making a significant profit on the sale, but he didn’t buy any stock. “I should have done some work on Apple…it’s not a complicated company.”

Still, despite the missed opportunities, Lynch doesn’t believe in chasing trendy stocks for fear of missing out, especially if he doesn’t fully understand the business. “You really have to be careful, look at the balance sheet,” he warned retail investors. “What is the reason the stock is going higher? ‘The sucker is going up’ is not a good reason.”

In order to make serious long-term gains, Lynch said investors should be looking for “a company that’s either a turnaround [story] or that’s going to grow” and then analyze its balance sheet to ensure its properly managed and doesn’t have too much debt. And while some on Wall Street have cautioned investors to remain defensive due to the potential for a U.S. recession, Lynch said “no one can predict the future” and what matters is properly evaluating each individual business before investing.

“You know, we’ve had 13 recessions since World War II and 13 recoveries,” he said. “I cannot predict the future, but this recession is so expected, so predicted, maybe it’s coming, but I don’t know.”