But these quotations also hint at two broader explanations for the millennial reaction: a generational narcissism and a generational need to be part of history, especially when its easy.

Let’s take the last one first. Millennials love to hurl themselves in the path of history. This isn’t exclusive to 9/11 — think of how they voted for Obama by record margins, then disappeared when the real work began — but it’s easiest to spot in examples involving the military. In another recent survey, conducted by American University, 12% of millennials said 9/11 made them more likely to enlist, but 26% said it made them less likely. And, without submitting to stereotypes — Keith Urbahn, the guy who broke the news of Bin Laden’s death on Twitter, is both a Yale millennial (class of 2006) and a member of the Navy Reserve — it’s safe to say that the millennials who do enlist don’t typically come from places like Yale.

Which brings us to narcissism. Millennials on Yale’s quad, at the White House and at ground zero didn’t think about how their celebrations might look to the rest of the world. They didn’t remember how they felt when Arab millennials celebrated the fall of the Twin Towers. They didn’t seem to recognize that 9/11 affected all Americans — we’ve all lost some shampoo in line at the airport.

Instead of considering this, the millennials decided to join history’s latest, greatest flash mob.