Peter Drucker, Harvard Business Review (2016). “The Peter F. Drucker Reader: Selected Articles from the Father of Modern Management Thinking”, p.59, Harvard Business Review Press
Peter F. Drucker (2014). “The Peter Drucker Collection on Managing in Turbulent Times: Management: Revised Edition, Management Challenges for the 21st Century, Managing in Turbulent Times, and The Practice of Management”, p.65, Harper Collins