In retrospect, it seems startling that people never imagined that a plane could be hijacked and crashed into significant target. Plane hijackings, after all, have been occurring for years. People seem to have assumed that hijackers would never crash a plane into a target because the hijackers would not want to lose their own lives. However, for years before 9/11, people in the mideast had shown a willingness to blow themselves up, as "suicide bombers," in order to achieve their goals. Putting 2 and 2 together here should not have been difficult, but, of course, hindsight is always 20/20.