Jordan Peterson is such a frustrating person to listen to.
He is so close to making a significant breakthrough and eventually writing a dynamite book about the nature and consequences of deep seated delusion, assuming that he learns at some point to reign his own.
His insight is wild and malformed, but there is a lot of promise there nonetheless.
Anyway, about the significance of 9/11. Jordan Peterson is at his best talking about psychology, but has a bad habit of allowing himself speak to audiences while bleeding into other subject matters that he just doesn't give nearly enough thought to.
We see that here. He skirts along the edge of the significance, but apparently he does not have a lot of experience with matters of History proper. He is in awe for the psychological impact of a specific historical event and doing a very good job of presenting that as the be-all end-all of the consequences, despite being obviously wrong. I believe that he sincerely fails to notice that he is neglecting to talk about the historical significance of the historical event. He is charismatic, one has to give the old devil that much.
So charismatic that we may easily end up forgetting that History deals with a perspective and scope that are not really very similar to those of psychology. That is significant here, because his discourse is very much fixated on a "what if" scenario that, from all indications, is pure fantasy.
9/11 was not a particularly avoidable event, no matter how ardently people attempted to convince themselves otherwise back in the day. It was the eventual consolidation of trends and forces that had been put into place for decades by the very specific needs and demands of people who are far too commited to keeping things predictable for anyone's good. People who knew what others expected from them and played along to the bitter end.
IMO the true greater significance of 9/11 is that it happened to be the immediate trigger event for the collective decision of how people worldwide would balance their fears with their idealism. The overall response was "by giving up and embracing those fears, destructively and irrationally as that might be".