This fall marks the 21st year I will be teaching college students about the September 11 terrorist attacks. It used to be that 9/11 was a trauma shared by everyone. Now it is a day that no one in my classroom but me remembers.

Educating successive generations of teenagers about the intelligence failures that led to that day has been a strange and surprising journey. At first, I struggled to find ways to take the emotion out of my teaching—to bring logical reasoning, historical perspective, and careful analysis to a moment that seemed to defy all of those things. Now I struggle to put the emotion back in, helping students who weren’t yet born when al-Qaeda terrorists attacked our nation understand the visceral context and swirling uncertainties that intelligence officials and policy makers faced.