How do strategic surprises happen? Lessons from 9/11

22 years ago, on September 11, 2001, the world watched in horror as two planes crashed into the World Trade Center in New York in one of the most spectacular terrorist attacks ever. Behind this immense tragedy, whose geopolitical consequences are still being felt today, lies the failure of the American intelligence apparatus, and the CIA in particular. Despite all the information at its disposal, the CIA failed to anticipate the attack. What explains this failure?