"March of Folly," a study by the historian Barbara Tuchman of history's costliest blunders, was lying open on the reading table a year ago when I first discussed the prospect of an American invasion of Iraq with my Syrian-born friend Raja Sidawi.

America was about to make a mistake of historic dimensions, warned Sidawi, who made his fortune in the oil business and now runs Petroleum Intelligence Weekly and other industry publications. He likened the Bush administration's implacable march into Iraq to Britain's mobilization for the deadly morass of World War I and America's self-inflicted wounds in Vietnam.

No, no, I told Sidawi. This time it could be different. The Arab world is beginning a period of upheaval and change, and good things will be impossible without the removal of Saddam Hussein. I still believe that, but I am haunted by my friend's words.

I visited Sidawi a few days ago at his penthouse on the Avenue Foch. The newspaper headlines were recounting the deaths of more American and British soldiers in Iraq, as the daily toll of ambushes and firefights continued. The war, it seemed, might only be beginning.

"I am sorry for America," Sidawi said. "You are stuck. You have become a country of the Middle East. America will never change Iraq, but Iraq will change America. To survive, you will have to develop a sense of irony."

This tragic sensibility -- the sense that in most instances, things do not work out as you might have hoped -- is generally lacking in the American character. Americans are an optimistic people: They have difficulty imagining the worst. That was why 9/11 was so shocking. Most Americans never considered that such devastation could be visited on them.

Arabs grow up in a culture where it is always best to assume the worst. Sidawi rattled off the list of wars and disasters that have afflicted the Middle East almost continuously since he was born in 1939. That is the bloody history in which America has now enmeshed itself.

"You will learn the culture of death," warned Sidawi. He believes Iraq will change America, as the ambushes that kill one or two soldiers are replaced by truck bombs that kill dozens. Staying the course will make America a tougher country, and a different one, too.

Sidawi decided that he wanted to leave that culture of death behind. In his youth, he says, he had been a "Don Quixote," a radical newspaper editor who dreamed of liberating the Arabs. But by his thirties he had concluded that the graveyards were full of Arab idealists, and he did not want to join them. So he willed himself to think like a "foreign observer" -- detached, objective, cynical. He even refused to teach his two daughters Arabic, to help them break free from the unending torment of the Middle East.

The slow transformation of American innocence is evident at the Defense Department's new Web site, www.defense.gov. Last week, there were some bits of yellow-ribbon sentimentality -- links to a "Support Our Troops" section where you could download patriotic posters or a special "Family Circus" cartoon captioned: "Thank you for protectin' all us kids!" But there were also stories about the carnage in Iraq, and thumbnail pictures that showed American soldiers fighting the bitter war against the remnants of the Baathist regime.

The worst possible outcome in Iraq would be for the United States to cut and run, leaving behind a California-size version of Lebanon. In that sense, Sidawi is right. Americans will have to develop a tragic sensibility to survive.

Perhaps the best way to begin is for President Bush to level with the American people about why we went to war -- and why we must remain. Evidence of weapons of mass destruction may ultimately be found, but the case was never persuasive. And the supposed intelligence about Iraqi links to al Qaeda was worse -- some of it close to bald propaganda. Even key allies in such countries as Jordan and Britain thought it was, as one top official delicately put it, "exaggerated."

In truth, America went to war to topple Saddam Hussein's regime. It's tragic to see how ill-prepared we were for building a new Iraq, but there is still time. America will lose some of its innocence as it descends into the Iraqi inferno. But in the process, Americans may develop a mature appreciation of their country's power, and its limits.

The churches of England and France are covered with the names of young men and women who died in faraway places fighting for king, country and empire. There are, alas, many more American names still to be memorialized from the Iraqi battlefield.