Human beings go through seven stages of grief. Hollywood goes through about three.

First, there’s the period of outright denial. Then there’s the longer, complicated moment of acceptance (and exploitation). Then finally a slip into amnesia — and a move on to the next tragedy.

Which has been exactly how Hollywood has dealt with — and, more often, not dealt with — the World Trade Center attacks.

It’s a particular act of artistic cowardice because the assault on the twin towers was not only a blow against America, but against the movies’ favorite metaphor — a symbol of personal growth, of economic opportunity, of possibility.

From the deeply wounded soldiers in films like “The Hurt Locker” and the emotionally exploitative images of “War of the Worlds” to the extreme interpretation of the Patriot Act in “The Dark Knight,” films touching on the events of Sept. 11 have shown the difficulty of bringing that day to the big screen.

In bad times, Manhattan was where immigrant kids became underworld bosses and vengeful vigilantes prowled the streets. In good times, it was where sailors went on the town, and even a Staten Island working girl could rise to the top.

It stood for a world that wouldn’t stand still, and so it became, for those fanatics marching backward toward the 11th century, a shining target on a hill.

Once its powerful symbol fell, though, it was Hollywood that ran. The movies even tried to pretend the towers had never even existed, cutting innocent shots of them from ready-for-release comedies like “Zoolander” and “Sidewalks of New York.”

As 2001 went on, entire topics became off-limits. “Collateral Damage” (whose firefighter hero loses his family to a terrorist attack) and “Big Trouble” (a comedy about an airport bomb scare) got bumped into the next year. Plans for an Adam Sandler farce featuring a Muslim terrorist — eventually made as “You Don’t Mess with the Zohan” — were pushed to the back burner.

In real life, images of that awful day’s horror, including the attack on the Pentagon, were everywhere. The assault on Manhattan, of course, predominated — not only because of the extensive live footage but because of what had fallen.

Yet Hollywood, oversensitive to criticism — or overprotective of profits — pretended it hadn’t happened.

It continued to pretend for five long years, letting the national conversation — about revenge, about freedom, about what price to pay for both — go on without it.

Finally, in 2006, two directors spoke up.

Paul Greengrass’ “United 93” — centered on the hijacked plane that passengers forced down in Pennsylvania — saluted everyday heroism. It was, for a director prone to conspiratorial thrillers, a tribute to simple civilian nobility.

Oliver Stone’s “World Trade Center” focused on the first responders. Abandoning his usual iconoclasm, Stone — himself a veteran — served up a solemn hymn to all in uniform who, when disaster strikes, run not from the danger but toward it.

Both films faced up to the tragedy, but neither movie was embraced by audiences. And so Hollywood quickly, abortively abandoned the story of an attack on America for stories of America on the attack.

Their efforts almost made you wish they’d go back to denial.

Although Hollywood’s films about the wars in Iraq and Afghanistan loudly sounded a rallying cry of “Support Our Troops” — unlike those of the Vietnam era, which seemed to hate both the war and its warriors — the stories were often just as critical, and as clichéd.

In “Redacted” (2007), soldiers rape and murder a young Iraqi girl; in the same year’s “In the Valley of Elah,” they come home to kill Americans. In “The Hurt Locker” and “Stop-Loss,” both released in 2008, vets turn self-destructive; in 2009’s “Brothers,” one terrified Marine executes another, under threats from his captors.

Yes, each new film began by praising our armed forces’ self-sacrifice; taken as single experiences, several of the stories were moving. But their cumulative effect only endorsed the old Nam “baby-killer” clichés — every veteran was a walking time bomb, traumatized not by what was done to him but by the terrible things he’d done.

Most of the documentaries were even worse, obsessed only with their own politics. (Michael Moore’s “Fahrenheit 9/11” didn’t even include footage of the towers falling — although it found room for images of Arab casualties in the invasion of Iraq.) What had happened at the World Trade Center — and why — was pushed off-screen.

Which may have been just as well, as Hollywood was far better about talking about 9/11 when it pretended not to be.

Steven Spielberg was the first to push things far — too far — in 2005 with “War of the Worlds.” Cluelessly crass, it appropriated sacred images — the stumbling survivors coated in ash, the sheaves of paper floating through a tombstone-gray sky, the hastily made “missing” posters — to amp up a shallow sci-fi remake. Yet its tasteless exploitation managed to evoke more of that September day than more respectful efforts.

Three years later, “The Dark Knight” subtly built on that. It may have been presented as just another superhero film — but with a nihilistic Joker who wanted to “watch the world burn” and a Batman ready to ignore every civil liberty to catch him, it caught the anarchy and paranoia of those times far better than many more “serious” dramas.

The very fact that images of that day could now be repurposed and exploited suggested that Hollywood was moving on for good. If so, many weary moviegoers seemed to think it was time.

Empty theaters

The few films that have tried to look back since have mostly played to empty theaters. The 2007 film “Reign Over Me” used the personal losses of 9/11 to explain a character’s breakdown; 2010’s “Remember Me” used the shock of that cataclysm to deliver a contrived third-act surprise. Both pictures flopped.

Their failure helped stop the trend. True, several producers are readying projects on the hunt for Osama bin Laden; a big-star version of the post-9/11 story “Extremely Loud and Incredibly Close” has a winter release date, in hopes of Oscar buzz.

But in reality, Hollywood has already moved on to the next national disaster — the economy.

As usual, it’s several years behind the actual event. And, as usual, it’s scared of the messy human drama, preferring to focus on upper-class heroes (“The Company Men”) and silly comedies (“The Other Guys,” “Horrible Bosses”). And soon, it will undoubtedly move on to the next topical catastrophe, whatever that might be.

But we won’t. We never will. We’re still here, 3,000 miles away from Malibu — and a fast PATH train away from two holes in our hearts.

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