John W. Gardner, the secretary of Health, Education, and Welfare under President Lyndon Johnson and later the president of the Carnegie Corporation of New York, wrote many books and gave many speeches about leadership. But perhaps his most influential was delivered on November 10, 1990 in Arizona at global business consulting firm McKinsey & Co.

In Harvard Business Review, Bill Taylor, the co-founder of Fast Company magazine, describes Gardner's speech, entitled "Personal Renewal," as "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." Taylor recounts the important lessons he took from Gardner's speech, the biggest of which was that great leaders stay great throughout their career by never giving up the practice of learning.

"There's a myth that learning is for young people. But as the proverb says, 'It's what you learn after you know it all that counts,'" Gardner told McKinsey that day in 1990. "The middle years are great, great learning years. Even the years past the middle years. I took on a new job after my 77th birthday--and I'm still learning."

Gardner passed away in 2002, but his lessons continue to be shared. Here are a few of the best quotes from his legendary speech.

Don't be interesting, be interested. 

"I'm not talking about anything as narrow as ambition. After all, ambition eventually wears out and probably should. But you can keep your zest until the day you die. If I may offer you a simple maxim, 'Be interesting.' Everyone wants to be interesting--but the vitalizing thing is to be interested. Keep a sense of curiosity. Discover new things. Care. Risk failure. Reach out." 

Don't stop learning. 

"Learn all your life. Learn from your failures. Learn from your successes, When you hit a spell of trouble, ask, 'What is it trying to teach me?' The lessons aren't always happy ones, but they keep coming. It isn't a bad idea to pause occasionally for an inward look. By midlife, most of us are accomplished fugitives from ourselves."

Learn how not to fail. 

"Of course failures are a part of the story too. Everyone fails. Joe Louis said, 'Everyone has to figure to get beat some time.' The question isn't did you fail, but did you pick yourself up and move ahead? And there is one other little question: 'Did you collaborate in your own defeat?" A lot of people do. Learn not to." 

Life can be endless. 

"Life is an endless unfolding, and if we wish it to be, an endless process of self-discovery, an endless and unpredictable dialogue between our own potentialities and the life situations in which we find ourselves. By potentialities I mean not just intellectual gifts but the full range of one's capacities for learning, sensing, wondering, understanding, loving, and aspiring." 

People move the world. 

"There is no perfection of techniques that will substitute for the lift of spirit and heightened performance that comes from strong motivation. The world is moved by highly motivated people, by enthusiasts, by men and women who want something very much or believe very much."