[afavour]

> The US was so complacent in their idea that nobody would ever attack them

I don't think that's true. There was an attempt to bring down the WTC in 1993 after all!

Authorities were taken by surprise by the method of attack. Hardly surprising since it hadn't been done before. Up until that point a hijacked flight almost always meant a ransom attempt, so you didn't shoot the plane down, you got them to land and began negotiations.

It's really easy to look back in hindsight and say authorities should have done X but there really was a great deal of uncertainty. It's not even clear what could have been done about the second plane.

[HumblyTossed]

None of that is even what I'm talking about. The people watching it, in real time, commenting on it, didn't even speculate that it could be an attack. Even after the second plane. That's complacency.

[snypher]

https://youtu.be/2ZwwCNoPa1w

Possible terrorist attack was mentioned by on air reporting before the second plane hit.

[jihadjihad]

It's not complacency, it's professionalism, and there are several counterexamples to your claim on the linked page.