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 Drucker, Harvard Business Review (2016). “The Peter F. Drucker Reader: Selected Articles from the Father of Modern Management Thinking”, p.8, Harvard Business Review Press
Peter F. Drucker, Frances Hesselbein Leadership Institute (2010). “The Five Most Important Questions Self Assessment Tool: Participant Workbook”, p.7, John Wiley & Sons