Nearly a quarter century ago, at a gathering in Phoenix, Arizona, John W. Gardner delivered a speech that may be one of the most quietly influential speeches in the history of American business — a text that has been photocopied, passed along, underlined, and linked to by senior executives in some of the most important companies and organizations in the world. I wonder, though, how many of these leaders (and the business world more broadly) have truly embraced the lessons he shared that day.

Gardner, who died in 2002 at the age of 89, was a legendary public intellectual and civic reformer — a celebrated Stanford professor, an architect of the Great Society under Lyndon Johnson, founder of Common Cause and Independent Sector. His speech on November 10, 1990, was delivered to a meeting of McKinsey & Co., the consulting firm whose advice has shaped the fortunes of the world’s richest and most powerful companies. But his focus that day was on neither money nor power. It was on what he called “Personal Renewal,” the urgent need for leaders who wish to make a difference and stay effective to commit themselves to continue learning and growing. Gardner was so serious about this learning imperative, so determined that the message would get through, that he wrote the speech out in advance because he wanted “every sentence to hit its target.”

What was his message? “We have to face the fact that most men and women out there in the world of work are more stale than they know, more bored than they would care to admit,” he said. “Boredom is the secret ailment of large-scale organizations. Someone said to me the other day ‘How can I be so bored when I’m so busy?’ I said ‘Let me count the ways.’ Look around you. How many people whom you know well — people even younger than yourselves—are already trapped in fixed attitudes and habits?”

So what is the opposite of boredom, the personal attribute that allows individuals to keep learning, growing, and changing, to escape their fixed attitudes and habits? “Not anything as narrow as ambition,” Gardner told the ambitious McKinsey strategists. “After all, ambition eventually wears out and probably should. But you can keep your zest until the day you die.” He then offered a simple maxim to guide the accomplished leaders in the room. “Be interested,” he urged them. “Everyone wants to be interesting, but the vitalizing thing is to be interested…As the proverb says, ‘It’s what you learn after you know it all that counts.’”

In these head-spinning times, even more so than when John Gardner offered his timeless advice, the challenge for leaders is not to out-hustle, out-muscle, or out-maneuver the competition. It is to out-think the competition in ways big and small, to develop a unique point of view about the future and get there before anyone else does. The best leaders I’ve gotten to know aren’t just the boldest thinkers; they are the most insatiable learners.

Roy Spence, perhaps the most interested (and interesting) advertising executive I’ve ever met, recently published a book called The 10 Essential Hugs of Life, a funny and moving take on the roots of success. Among his wise and folksy pieces of advice (“Hug your failures,” “Hug your fears,” “Hug yourself”) is a call to “Hug your firsts” — to seek out new sources of inspiration, to visit a lab whose work you don’t really understand, to attend a conference you shouldn’t be at. “When you’re a kid,” he says, “every day is full of firsts, full of new experiences. As you get older, your firsts become fewer and fewer. If you want to stay young, you have to work to keep trying new things.”

Spence cites as one of his inspirations management guru Jim Collins, who, as a young Stanford professor, sought advice and counsel from his learned colleague John Gardner. What did Spence learn from Collins? “You’re only as young as the new things you do,” he writes, “the number of ‘firsts’ in your days and weeks.” Ask any educator and they’ll agree: We learn the most when we encounter people who are the least like us. Then ask yourself: Don’t you spend most of your time with people who are exactly like you? Colleagues from the same company, peers from the same industry, friends from the same profession and neighborhood?

It takes a real sense of personal commitment, especially after you’ve arrived at a position of power and responsibility, to push yourself to grow and challenge conventional wisdom. Which is why two of the most important questions leaders face are as simple as they are profound: Are you learning, as an organization and as an individual, as fast as the world is changing? Are you as determined to stay interested as to be interesting? Remember, it’s what you learn after you know it all that counts.