If I had to name the single characteristic shared by all the truly successful people I've met over a lifetime, I would say it is the ability to create and nurture a network of contacts.

Although I never met David Rockefeller, he certainly would have fit in this category. When he died in March 2017 at the age of 101, Bloomberg News revealed that he had an "electronic Rolodex" of 150,000 people. The Wall Street Journal recently reported it was 200,000.

He was a master networker during his two decades as the head of Chase Manhattan Bank and 60 years of being involved with the Council on Foreign Relations.

In my corporate speeches, I often ask the question: What is one of the most important words in the English language? I add that if all of us understood this word just a little bit better, we would be way more successful than we already are. That word is "Rolodex," which of course is now referred to as a "contact management system."

My father, Jack Mackay, who for 35 years led the Associated Press in St. Paul, shared his secret with me when I was 18.

He said, "Harvey, every single person you meet the rest of your life should go in your Rolodex file. Write a little bit about that person on the bottom or the back of the card. And now, here's the key — find a creative way to keep in touch."

That's what I've been doing ever since. I now have nearly 20,000 names in my electronic Rolodex file, a far cry from David Rockefeller, but still critical to my career. The contacts I've made over all these years are why I've been writing this nationally syndicated column for the last 24 years.

My Rolodex was instrumental in launching my publishing career. Let me explain. In 1988, there were roughly 2 million "wannabes" — people who wrote manuscripts. Roughly 200,000 books were published. Of those, only a small percentage were business books. If you are a first-time, unknown author like me and you write a business book, you want to get it published. But a work by a debut author would get a print run of 10,000 hardcover books, at most. That's it. Tom Peters, "In Search of Excellence," 10,000 copies; Ken Blanchard, "The One Minute Manager," 7,500 books.

This is why it was so tough to get started. There were 5,000 bookstores back in the '80s and '90s, which means an average of only two books per store if they print 10,000 copies.

I had written a book titled "Swim With the Sharks Without Being Eaten Alive." I wanted the publisher to print a lot of books so they would promote it and not run out of copies. I scheduled a summit meeting with publisher William Morrow and Company — the CEO, president and vice president of national sales. About 45 minutes into the meeting, I asked for the order. I said, "I would like you to seriously consider printing 100,000 hardcover copies of 'Swim With the Sharks.' " We were on the 37th floor, and they basically told me to jump. The VP of national sales closed his notebook and said, "Thank you very much, Mr. Mackay. Obviously, we're not going to get together." Then he basically screamed, "Who are you coming in here asking for 100,000 copies? We only print 10,000 copies for any first-time unknown author."

I'd brought in two humongous briefcases and took them out. Inside were two huge Rolodex files, 6,500 names at the time. I started to go through them: "Pillsbury, 18,000 employees. We do business with them. Maybe they'll read the book and pass it along. General Mills, 23,000 employees; Cargill; 3M; here's American Express." I went to the second Rolodex file. "We do business in six countries, France, Germany, Spain ... maybe it'll be an international bestseller."

Three weeks and three meetings later, William Morrow published 100,000 hardcover copies of "Swim With the Sharks." And it became a New York Times No. 1 bestseller.

Did I know when I was 18 where my contacts were going to come from? Do any of you know where your contacts will come from five, 10 or 15 years from now?

Our lives basically change in two ways — the people we meet and the books we read. Trust me; the people you meet every day are extremely important in building your network.

In my entire career, I have never once heard a successful person say he or she regretted putting time and energy into keeping their Rolodex file.

Mackay's Moral: When you work on your network, your network works for you.

Harvey Mackay is a Minneapolis businessman. Contact him at 612-378-6202 or e-mail harvey@mackay.com.