Unlike the Kennedy assassination, it is not etched into my mind. I guess because I think the first thing I saw was that an airliner had crashed into the World Trade Center.
At the time I did not know the buildings would collapse or that it was terrorism. As soon as the second one hit, everyone knew what was going on.
I still was surprised that they collapsed. I knew that during WWII a B-25 had crashed into the Empire State Building. It did some damage but was fairly quickly repaired. I had no idea just how much fuel those airliners held.
B-25 - Maximum Takeoff Weight - 34,000 lbs
767-200Er- MTOW - 395,000 lbs.
At least 11X the mass of the B-25 and 3X the speed when it hit. It probably would been comparable to crashing 100 B-25’s into the building simultaneously.