My first thought when a coworker announced it (she was listening to the radio with headphones) was basically "It finally happened" because I'd been amazed for years that I'd never heard of someone hijacking a plane with the intention of hitting a large structure -- particularly a building. I assumed either it had happened and I didn't hear about it or there were procedures in place that made it difficult or impossible. I have a hard time believing the entirety of the powers that be didn't think anyone would try it. But I think I was probably making an ignorant assumption and just "got lucky" that it looked, in hindsight, like I knew what I was talking about. Say enough shit and something's bound to be spot-on eventually. I'm still really surprised if it's true that they didn't think someone would seriously try it.