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After the attacks on the World Trade Center, Americans — and particularly New Yorkers — were told that we needed to go about our lives as we normally would to demonstrate to the terrorists that they hadn't won.

Shop, officials told us. Go out to eat. Travel. As our mayor then, Rudy Giuliani, said in a speech to the United Nations a few weeks after the attacks:

"For individuals, the most effective course of action they can take to aid our recovery is to be determined to go ahead with their lives. We can't let terrorists change the way we live. Otherwise, they will have succeeded. In some ways, the resilience of life in New York City is the ultimate sign of defiance to terrorists."

Their goal was to scare us and change us. We had to show them that neither had happened. We had to show them.

A couple of weeks after the attack, I went to dinner at a restaurant in the Meatpacking District, just a mile or two from ground zero, where the massive mound of rubble where the twin towers once stood was still simmering. You could smell the metal in the air.

Hugh Hefner was also at the restaurant that night, surrounded by a group of women who looked remarkably similar. Other women occasionally made their way from their tables to his, smiling and laughing and posing for pictures.

I thought for a moment: Could there be a shoulder shrug any more symbolic and uniquely American than Hefner hamming it up in a banquette full of blondes? Was this what "not letting the terrorists win" looked like?

No, it wasn't. This whole battle of optics was a fiction. Of course the terrorists had achieved their goal of forever altering us. I, like most Americans, would have to admit that I, too, was irrevocably changed.

Sept. 11 shattered our sense of safety, our belief that the oceans on our coasts served as barriers and protection against many forms of aggression.

We lived in a free society, and it was those very freedoms that rendered us vulnerable.

The attacks also unleashed the worst in us. I often think about the days that followed, the rising in me of a burning desire for vengeance, an impulse I didn't know I harbored and one that disturbed me.

The war hawks saw that desire for vengeance in all of us, and they salivated. This was their chance to fight a war they wanted, a war that only just now has come to a close.

But the attacks also made many Americans fear their neighbors — mostly Middle Eastern ones — in a way they never had before. We had not just been attacked by 19 hijackers, but by a culture, by a religion. Innocent Americans were made guilty by association.

People from the Middle East were watched, warily, and sometimes even surveilled.

People were afraid, and they projected that fear in the worst ways. Osama bin Laden was still alive. The threat was still real. Many people believed that another attack was imminent.

We learned to live with this ambient fear. It became the norm. My children were 7 and 4 on Sept. 11. They don't remember anything before the war on terror. But from then on, they would face constant reminders of the new and terrifying reality we'd all been thrown into: with moments of silence for those who had died in the attacks, and classmates who had lost parents. For a vast majority of their lives, we have been in wars that grew out of that one day's attacks.

Yes, it changed us, fundamentally.

And as a USA Today/Suffolk University poll released last week found, "The sense among Americans that the Sept. 11 attacks permanently changed life in the U.S.A. has grown, not faded — as the 20th anniversary of 9/11 approaches and a new peril threatens the nation."

We are only in retrospect coming to comprehend the profundity of what happened 20 years ago, when we saw people leap to their deaths to escape the flames — only now coming to fully appreciate the meaning of those crumbing buildings or the ghostly apparitions who silently trudged home across the bridges, their bodies covered in ash.

In one meeting in the New York Times' newsroom on the day of the attacks, I heard an editor make the analogy that it was like one of the arms of the city had been ripped off. But she was wrong: This was not an attack on a limb, but on life, on the heart of the city and the country.

Bin Laden had showed us that he could touch us — and make it hurt — in our centers of power. Just 19 men armed with box cutters, willing to give their lives, could change ours and plunge us into a war that cost trillions of dollars and thousands of lives.

People of my generation will never know again what my children's generation only tasted: an innocence and obliviousness about threat and danger. I am — we all are — covered forever with a bit of the ash from those towers.