The attacks of 9/11 have faded into history -- for some, a dimming memory; for ever more people, an event that happened before they were even born. Yet the impact of 9/11 is with us today in innumerable ways, notably the Afghanistan "forever" war. And, nineteen years on, the fundamental lessons of 9/11 have not been learned. What is the full significance of that tragic event? What moral-philosophic lessons should we draw from it?