But going back to that day again, we are reminded of humanity's greatest lesson on earth – to learn from our mistakes.
Newly posted audio files online depict the horror of 9/11 unfolding in the sky and our inability to deal with it as effectively as we would have liked to.
The audio files paint the inability of what was seen as the world's ''most powerful nation'' to counter the threats as air traffic controllers struggled to follow the faint tracks of hijacked planes, fighter planes tried in vain to chase them down and a flight attendant made a desperate appeal for help.
The sound files add a layer of emotion to previously published transcripts, as puzzlement and frustration seeps into the voices of controllers, military commanders, and even pilots watching the attacks from the sky. There are shouting and ringing phones in the background -- the soundtrack, usually omitted from written transcripts, of a nation suddenly at war.
In one chilling excerpt, screaming and a shouted "Hey!" is heard over the radio as hijackers storm the cockpit of United Flight 93. That's followed by a strange, strained cry. Stunned controllers and other pilots discuss the sounds, trying to make sense of what they heard.
Most of recordings come from the FAA and are of controllers and the military liaisons working with them. But some come from other sources, including a phone call that Betty Ong, a flight attendant on American Airlines Flight 11, placed to the airline.
"Somebody's stabbed in business class, and, um (sic) I think there is Mace that we can't breathe," Ong said. "I don't know, I think we're getting hijacked."
That chilling admission summed up that day and the events that unfolded soon after.
The military had only learned about the hijacking of Flight 11 nine minutes before it crashed into the World Trade Center, and was never notified about the other hijackings before those planes crashed. That was how unprepared America was on that day.
"The confusion on that day is something that we sometimes forget about," said Andrew Gimigliano, editor-in-chief of the Rutgers Law Review.
"The idea that hijacked planes would be used in that manner just was not something that people were thinking about, and this is really illustrative of what the real tenor was on that morning."
Image: In this September 11, 2001 file photo, United Airlines Flight 175 approaches the south tower of the World Trade Center in New York shortly before collision as smoke billows from the north tower. (Photo credit: AP)