Jim Collins wrote the forward for The Daily Drucker, edited by Joseph A. Maciariello, based on Collins frequent visits to Peter Drucker during the last years of his life.

Jim Collins.com: The Daily Drucker, 2004-Aug-3

At the end of my day with Drucker in 1994, we pulled up to his home after a meal at his favorite local restaurant. "How can I thank you, how can I repay you?" I asked, knowing that the value of a day with Drucker was incalculable.
"You have already repaid me," said Drucker. "I have learned much from our conversation today." That's when I realized that what ultimately sets Peter Drucker apart is that he does not see himself as a guru; he remains a student. Most management gurus are driven to say something; Drucker is driven to learn something. Drucker's work is interesting—he is interesting—because, to borrow a phrase from the late John Gardner, he remains relentlessly interested.

"Just go out and make yourself useful," he finished. Then, without another word, he got out of the car and walked into his modest home, presumably back to his typewriter…