Growing up in school, there were always two events that history teachers gave as examples of moments where everyone remembers where they were when it happened: the moon landing and when President Kennedy was assassinated. My junior year of high school, another one of them happened.
My day began, ironically enough, in history class. It was a double period for some reason, and we were watching The Mission as we were studying South America. Because we were shut in for a couple hours and they made no announcements over the PA, I didn't hear about the events unfolding until later than the rest of the school. A friend stopped me in a stairwell to say that a plane had hit the WTC and a bomb had gone off at the Pentagon. I waived her off, saying that a plane had hit the Empire State Building before and it was probably going to be okay. When I got to biology class, the TV was on and I could see that this was a bit bigger of an ordeal. As events progressed and the towers fell, I was doing day 2 of a bio lab involving dangerous chemicals because it was time sensitive and the teacher said there wasn't going to be time to redo the whole multi-day experiment later.
We remember events like 9/11 because we can't help ourselves. Things that shake us to our cores leave indelible imprints on our souls. It's part of the human condition. We remember them to honor those who died in innocence, who died trying to help others, and who have since died to bring justice to the organization that sponsored the attack. We remember to make sure we have learned lessons that can prevent similar things from happening in the future.
We remember because time passes inexorably and mercilessly into the future. I have teased my parents about how I wasn't alive when they talked about the moon landing or the JFK shooting. That shoe's now on my foot. My wife is a musician, and she has taught students who have told her about learning of 9/11 in history class. Anyone who is 14 or 15-years-old probably has no memory of it when it happened, and those younger certainly don't. For good, ill, and indifferent, September 11, 2001 changed this world, and it hasn't gone back to how it was. The youth need to know why because they will one day inherit this world that will still bear that scar.
Today is a day for reflection and remembrance, but it's also a day for passing it on. We can't ever let that day disappear from memory, lest future generations be doomed to repeat it.