By Richard Allen Greene
BBC News, Washington
John Yates was standing with four other men on a beautiful Tuesday morning five years ago when a plane smashed into his building - the Pentagon.
He was burned over more than a third of his body. He has only partial use of his left hand. He still has nightmares.
But some might say he was one of the lucky ones. He was the only one of the five men in that group to survive.
Five years later, he says what happened that day "is with me every day, every second. But it is not who I am."
He still works in the Pentagon, and it is when he talks about returning that he is most overcome with emotion.
"Physically I was fine. Mentally I was a wreck," he says.
"I maintained a database of people and their security clearances. I had to delete the names of my friends who were killed that day."
The day has permanently altered his life, he says.
"I don't take for granted that I'm going to live another day. My wife never lets me leave the house without saying: 'Be careful'.
"I never leave the house without saying: 'I love you'."
Mrs Wagner dislikes what she sees as the anger of "Never forget"
But while the attack on the Pentagon is still vivid in his mind - and scarred onto his body - Mr Yates says that is not true for most Americans.
"Unless you were personally involved, most people forget about it until this time of year.
"I tell my story so people won't forget. We should never forget."
"Never forget" is a frequent refrain among survivors of 9/11.
But it is one that Debra Wagner does not much care for.
Mrs Wagner, who was standing just one floor above John Yates in the Pentagon on 11 September 2001, wants the slogan to be "Always remember".
"I want them to remember the people who were in the Pentagon and the Trade Center and that field - the souls, the lives, what they brought to us.
"'Never forget' seems angry, a command. 'Always remember' is positive. It's an option," she says.
Memorial to brother
It is an option Jim Laychak has taken to heart.
His brother David was on American Airlines flight 77, the plane that hit the Pentagon.
Mr Laychak's memorial work is part of "looking after his little brother"
Jim Laychak is now president of the Pentagon memorial fund, which is raising money to build a commemoration at the site.
He agrees with Mr Yates that people who were not directly affected on 9/11 have largely moved on.
"It's tough for people to stay involved. Life goes on."
But, he says: "We have to remember how we felt that day, that horrible sick feeling when I realised my brother wasn't coming back."
And, he adds, people need to remember the positive aftermath of the attacks as well, "the compassion, people wanting to come together and support each other".
Losing his brother has changed his life, Mr Laychak is certain.
"You can't help but not sweat the small things. You think, 'What can I have an impact on?' For me, it has been the memorial."