It was a clear and sunny morning in Philadelphia on Tuesday, September 11, 2001. The kind of morning that makes you believe the world is orderly, predictable, even beautiful. A cold front had swept through the night before, leaving behind crisp air and cloudless blue skies. I was in Bristol, Pennsylvania, teaching a corporate class on Operational Excellence — twenty-two  scientists, engineers, and managers from across the world gathered for their Six Sigma Black Belt training. We had barely begun the session when the news arrived: a plane had struck the North Tower of the World Trade Center at 8:46 a.m. Seventeen minutes later, the second plane hit the South Tower.