Thanks Lyn. I can only aspire to write as precisely, concisely, and as engaging as you. Chapter 15 is a veritable masterpiece. Being an engineer myself, I appreciate the no-nonsense diagrams like the one below that conveys the overall dynamics of the system. And your simplified model of Mary, Sara and their two banks succeeded in loading the model into my working memory so I could work with it conceptually in my mind as a whole. You’ve done a great service to society.