This morning Charles, in the comments of my original post, provided an answer "Those who do not remember the past are doomed to repeat it"
This afternoon Ace ( @AceofSpadesHQ ) provides another in the form of this link, uncensored coverage of 9/11 as it was happening.
Now I would like to provide a third answer - In general Americans are pretty gregarious. We like most people we meet and we assume that they like us. We have to keep reminding ourselves that isn't true. We may be friendly, We may like you (France, Germany, Russia, Kuwait, whoever...), but that doesn't mean you like us. We can't forget that again.
In the words of General Mattis -
“You cannot allow any of your people to avoid the brutal facts. If they start living in a dream world, it’s going to be bad.”
This is kind of America's place in the world now. I don't think most people like it but I think the majority of us recognize it.