This is part of a continuing series by FOX News of unique perspectives on what it is to be an American.

For nearly every American, the scars from September 11 still run deep. On this generation’s “day of infamy,” the terrorists who attacked the U.S. seven years ago permanently changed the trajectory of American history.

Ken Krimstein, a longtime resident of New York City, recalls taking his son Milo to his first day of kindergarten on the day of the attack. He says 9/11 changed his ideas about what it meant to be an American and raised his awareness of the ideals for which this country stands.

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For Krimstein, 9/11 was the defining moment in his American story.

“I had just dropped Milo off when my wife called me and said that a plane had hit the World Trade Center,” Krimstein said. “I remember thinking that it must have been one of those small Piper Cubs, like the ones that had hit the Empire State Building a few times before, so I continued on to work.”

When he emerged from the subway, Krimstein said he began to become suspicious when he noticed people in the street with their car doors open and their radios on full-blast.

“I was on Sixth Avenue, which runs all the way downtown, and I overheard a radio mention something about a hit at the Pentagon. And then I looked down Sixth — and I remember this part because it was such a clear and beautiful day — and all I saw was a huge plume of smoke around the Twin Towers. The only way to describe it is surreal.”

After watching the first tower collapse on television while at work, Krimstein decided to get his son.

“When I got to Milo, he was really disappointed and didn’t understand what was happening,” Krimstein said. “He was really affected by it, and I think he could sense the sadness in people’s hearts, even if he couldn’t fully grasp what was going on.”

From that point, Krimstein said, things just became “stranger and stranger,” as phone service went out and the city buckled under the weight of the day’s events.

Krimstein, his wife and family made it home safely, and they spent the rest of the day watching the events unfold on television.

As he watched, Krimstein was struck by just how “truly lucky” he was. He had often done work in the World Trade Center, as he served as a former representative for his company to the Port Authority, which had offices in Tower One.

“I remember thinking to myself that this must have been how the British felt during the Blitz in World War II,” Krimstein said. “As Americans, we had never really experienced that kind of a civilian attack on the home front. That brought it home for us and pulled us onto the world stage in a way we had never really been.”

In the days after the attack, Krimstein said he felt an overwhelming desire to hang an American flag in his home, something he says he probably would not have done before the attacks. So he ran down to a “25-cent store,” bought a small flag on a wooden stick and taped it outside the window of his apartment.

“I think I wanted to hang the flag so much because I just kept hearing in my head over and over again that we had been attacked, that what we stand for — our freedom, our ideals — was under siege,” he said. “I was really struck by how much of a threat freedom in our society was to some people.”

In the weeks after 9/11, Krimstein noted that patriotism and American pride were felt more than ever in his Upper West Side neighborhood and throughout the city.

“When you scratch the surface, this neighborhood is really a flag-flying place,” he said. “We really treasure a diversity of opinion, and I think that we are aware that this is one of the only places on Earth that it could flourish in the way it does.”

It’s that respect for freedom that Krimstein said is a unifying factor in every American story.

“I think that all Americans feel a sense of potential here that can be fulfilled,” Krimstein said. “Our country is one of the great experiments in human history — others have dipped their toe in a society like ours, but there is nowhere else that you can really be free and live out your own individual dreams.”

Since the attack, Krimstein said that he has made a more concerted effort to teach his three children about freedom and the heavy price at which it can come.

“As Americans, we can be oblivious so often until something so violent happens and we realize that we have been taking it for granted,” he said. “Freedom is the highest evolved state of civilization that we have, and it can’t be taken lightly.”

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