People cheer and wave U.S. flags outside the White House Sunday night as President Obama delivers remarks to the nation on the death of Osama bin Laden. (JIM YOUNG/REUTERS)

This is the question that anyone over the mental age of 30 posed to me after Sunday night’s ebullience in the streets.

Why were there keg buses and teens on stilts? Why was everyone chanting “USA! USA!” as though this were some sort of pep rally? Why were there crowds? And why were the crowds so young?

Is it simply that we will take any excuse to party? I don’t think so. And this is coming from someone who admittedly, throughout college, threw annual parties to celebrate the anniversary of the first use of trained dolphins in a military operation.

You don’t understand, I tried to tell them. Osama is our Voldemort. He’s our Emperor Palpatine. He is the Face of Evil, a mythical holdover from when we were too young to realize that evil has no face.

After all, our generation is generally not allowed to call anyone evil. No one is evil, they told us. They just had weird childhoods.

Hitler got rejected from art school. Jared Lee Loughner was mentally disturbed. Even Darth Vader had some sort of upset in his childhood, with midi-chlorians, or something. We grew up drowning in nuance.

But Osama was pure evil. He was an acceptable target. And this was a relief. In our guts, we are accustomed to simple villains. In every story that has latched onto the popular consciousness, there is a Big Bad, a nemesis. Evil has a face. Palpatine. Voldemort. Sauron, although that would be less a face than an eye.

So for people my age, the idea that you would greet the news of Osama’s demise with anything short of unmitigated exhilaration is ludicrous. Call up the Ewoks and get the bonfires started. Gather the, er, wizards, for the wizard banquet. We got him. The Big Honcho. The top cheese. The chief muck-a-muck.

This capture puts a cap on half our lives. We beat this level.

It has long been our generational inclination to see life as a video game. Challenges to be overcome. Negotiations to be mastered. New gadgets to be acquired to help us overcome the challenges ahead — iPhones, anyone? Each level is controlled by a boss, a malignant figure who must be defeated for you to progress. And Osama was one such figure.

Sure, it’s a juvenile view. Sure, now people are coming out with studies that say it’s actually beneficial to play video games — which tells you only that the people who grew up with video games are old enough to conduct studies.

But the problem with a world viewed through a video game lens is that you have the idea that if you beat the boss, you will end the game. Osama is the Big Boss, the Level Master of the Ultimate Level, the diabolical Waldo. He was the dragon that lurks at the end of the final corridor. And we got him.

Of course we expect to celebrate.

For most of us Millennials, Sept. 11 was when we lost something. Not innocence, exactly. It wasn’t simply the first dawning of tragedy in our lives. It was the “Black Swan” before those psychotic ballerinas, the one salient incident that indelibly altered the way we saw safety, privacy, probability. It crystallized our characteristic, semi-contradictory generational attitude: optimistic fatalism.

“Terrible things happen,” we said. “But they happen at random, and without warning, in the most apocalyptic fashion possible, and those charged with preventing them cannot always succeed. So why worry? We must live our lives, and that means forgetting that such things can and do occur.” No wonder irony comes to us so naturally.

But there was a flip side to this horror, even then: a moment of rallying. As Katherine Miller has suggested, we continue to long for that moment, post-Sept. 11, when the country gathered around itself. We measure ourselves against that time, when, for a few weeks, we were all Americans first, and there was a run on flags and yellow ribbons. We want to be just Americans again. And that means rallying in the streets with strangers in the aftermath of a defining moment. We did it after the 2008 election. And now the other shoe has dropped in the battle against terror, and we flooded the streets to see if it would happen again.

But it couldn’t. That’s why the revel felt unseemly. It was simply the celebration of the death of one man, not a complete victory over any ultimate evil. Even as we cheered, we knew better. For us at 12 and 14, Osama was a reassuring monster. He was the face behind the random terror of the universe, the dragon we could slay and beat, the Boss of the Level. Now we understand that we have scorched the snake, not killed it. We know the difference between a hydra and a dragon.

But there is still that 12-year-old inside us, exultantly staring down the reactor shaft where we just tossed the Emperor.

Of course we want to party.