I finished a three-hour binge of racing, clicked off my Playstation 2, and … it was over. My compulsion had vanished. I still enjoyed the game, and had plenty more challenges to complete. But I didn’t need to play it any more. For some mysterious reason, Burnout had suddenly released me from its talons.

This is one of the abiding mysteries of games: Why do they let us go so suddenly? Every gamer I know describes the same abrupt drop-off, totally unexpected, arriving after hours or even weeks of feverish play. It is like a curious, unintentional form of cold turkey. You wake up one day fully expecting to spend another four hours in an eye-glazed stupor, only to discover that the thrill is gone.

Now, I’m not describing the “end” that comes when you complete a narrative game. In that case, it’s obvious why you’d stop playing. I’m speaking of the open-ended addictions — including online worlds, puzzle games, sports titles or Xbox live play — where you theoretically ought to be able to play ad infinitum.

I called several of my hard-core gamer associates to see what they think. Jonathan Hayes, a forensic pathologist in New York, regularly falls hard for gorgeous-world games like Ico, and recently he was swallowed whole by Resident Evil 4. He thinks the reason he stops playing a game is that he’s unwrapped every skin on its onion.

“You kind of see through the game to its underlying mechanics,” Hayes says, “and it suddenly seems no longer worth the investment of time.” This is much like what Raph Koster argues in his Theory of Fun: We humans seek constant novelty, so only gameplay that has nearly infinite permutations — like chess — can hold our attention forever.

And not many games rise to the complexity of chess. Indeed, one of the reasons it’s hard to get there is that there’s a paradox built into success. The better a game, the longer we play it — and the longer we play it, the more likely we are to notice tiny, subtle flaws in the game design. “For a while, with a really amazing new game, it’s all you do, all you think about,” says Luke Smith, who writes for the game blog Kotaku and recently has spent weeks fanatically rolling a level-60 character in World of Warcraft. “But then it’s balance issues, buggy play, poor online optimization. You keep trying to ‘make it work,’ and it won’t.”

Perhaps a game “ends” because teensy frustrations build up like plaque in our brains — until one day we suddenly rebel, and our attention shifts. In fact, this might be part of the reason I finally ended my servitude to Burnout. I hit upon a class of vehicles that I couldn’t perfectly control, and the joyful sense of mastery — the cybernetic loop that made me one with the machine — was suddenly tainted.

Though it’s also true that our addictions aren’t always, or even chiefly, about the games. Sometimes the forces that drive us into the arms of a game — and then release us from its grip — are in ourselves. Greg Sewell, a friend of mine, has been swept up by everything from Quake to “casual games” like Blix and Collapse; he thinks his periods of addiction are driven as much by the high quality of the games as by the occasionally crappy quality of his life. His peak gaming moments occurred as a way of avoiding his thoroughly cipher-like dot-com jobs.

“For me, the obsession is sometimes a coping mechanism — with a job that is boring, or some other life rut. And the obsession seems to end when the boredom ends or the situation I’m avoiding sorts itself out,” he says. He compares it to the emotional curve of a breakup. You pick an album that seems to embody your woe — then play it over and over and over. When the hurtin’ ends, the album instantly goes into the dustbin.

Indeed, top-40 hits are the only pieces of pop culture that behave like games. They flare brilliantly, demanding incessant and constant replay — until one day when we suddenly can’t abide them. Virtually no other forms of entertainment suffer this same drastic drop-off. When we fall out of love with TV shows and comic books and favorite writers, our attraction peters out. (I faithfully watched Alias for three seasons, and then slowly drifted away as the fourth season’s scripts got progressively duller.)

Conservative pundits have long fretted over the addictive quality of games, of course. But maybe the psychological curve of addiction is the ultimate tribute to the medium. They’re a form of culture so intense and delightful that we only have two options — delve in wholeheartedly, or walk away.