On Sept. 10, 2001, this nation was over a quarter century past its last real crisis. This is not to say the intervening years were uneventful: they were not. Those years saw three attempted presidential assassinations, a shuttle explosion, an impeachment, and sundry hostage takings, military actions and political scandals. But there had not, since Watergate, been a true "crisis," no event of the kind that shakes a nation, that stops it cold and takes its breath and makes it anxious about its future.

In this, the quarter century that ended five years ago was an aberration. Previous generations of Americans had come of age with reminders of life's true nature breathing close enough to stir the hairs at the nape of the neck. From the Great Depression that put the nation on the skids in the 1930s, to the sneak attack that plunged it into war in the 1940s, from the 1960s when every day seemed to bring fresh outrage — assassinations, riots, a step to the brink of nuclear war — to Watergate and the subsequent fall of a sitting president, and from there to the Cold War that hung over more than 40 years of American history like a pall of smoke, we were a nation too frequently made to know that life does not play fair.

By Sept. 10, 2001, we had largely forgotten this truth. Or, more accurately, we had enjoyed the luxury of not being reminded for a very long time.

It was the last day of the good old days and we didn't even know. Not that the days were good and old. Not that they were doomed.

But then, you never know the good old days when you are in them. On Sept. 10, 2001, the Cold War was 10 years past, 17-year-olds were becoming Internet millionaires and we thought a crisis was a president receiving oral sex in the Oval Office.

We had not yet seen people jumping from flaming skyscrapers. We had not yet seen office towers crumble to the ground on live television. We had not yet seen dust-caked people wandering the streets of our greatest city. We had not yet seen an airplane sticking out of the Pentagon. We had not yet seen wreckage in a Pennsylvania field. We had not yet seen men and women in badges and uniforms rushing forward into chaos and smoke and a certainty of death.

We had not yet seen. So we could not yet know.

On Sept. 10, 2001, such sights as those — never mind the attendant feelings of fury and terror — were unthinkable. As in, literally unable to be thought, unless in the context of a Stephen Spielberg movie, a Tom Clancy book, some artist's artifice by which we gave ourselves the pleasure of a good, hard scare, a shiver up the back in the heat of a summer's day. But real? Not in a million years.

On Sept. 10, 2001, we were innocent. And that seems a purely strange thing to say because innocence is the commodity we were repeatedly assured we had lost. We were told this in 1963, when John Kennedy was murdered, in 1974 when Richard Nixon resigned, in 1993, when the World Trade Center was bombed.

But innocence, it turns out, is a renewable commodity. That's heartening. Also troubling, because if you can have it again, it can be stolen again.

No, check that. It will be stolen again. That's the lesson of these last five years, that there is no vacation from history, no finish line you cross where you can raise your arms and lower your guard.

Chaos is not the aberration. Respite from chaos is. And being human means molding yourself to that reality, finding a way to live in the spaces chaos leaves.

On Sept. 10, 2001, we had forgotten that we once knew this.

That last day, like every day, the sun came to America first on the rugged coast of Maine and began its slow arc across the country. Down below, we worked, watched television, checked homework, got dinner on. The sun left us in the Pacific, the sky turning dark above a pendant of American islands.

On Sept. 10, 2001, we went to bed. We slept in innocence.

And then the morning came.

Leonard Pitts Jr., winner of the 2004 Pulitzer Prize for commentary, is a columnist for the Miami Herald. Reach him at lpitts@miamiherald.com.