I turned on the television the moment the second plane hit, and my jaw hit the floor.
As the day unfolded, I was blown away at both how the attack played out, and especially how exactly this attack was already being discussed for almost a year leading up to it, without anyone actually acting on the risk.
I see the entire thing as being one of those "Oh, there's been talk, but nothing like this would never happen to us," until it does.
Compare this with Covid19, the US having already known years ago that a pandemic was a matter of when, and then cutting funds and pretty much all mention of the risk until the risk became reality, and then passing the blame to the previous government, and finally pretending it's not such a big deal after all, unless it means criticizing the other party more.
EDIT: Later, I worked at Goldman Sachs and when I did a project in Asset Management, my working station was on the 33th floor overlooking where the Freedom Tower now stands, and I could see the outlines of the Twin Towers. Super eerie.