Whoops. "You know what? The babies cry a lot in that game," she says. "So it's crying while I'm trying to juggle everything else, like getting the parents to work and making sure they clean the house.” After a few hours of domestic chaos, her virtual baby was whisked away by a digital caseworker. "I was devastated! I was sure that I wouldn't be able to handle a real baby," Craig laughs. She kept playing, though, and by the time her actual baby arrived, she felt like a pro. "My family thought I was nuts, but I swear it got me through the pregnancy," she says.

At first glance, The Sims is an unlikely hit. It doesn't shred your dendrites with cutting-edge 3D graphics. You don't blast aliens with plasma guns, drive high-speed race cars, or get to play basketball against the Knicks. Yet this year, it became the best-selling computer game in history, with over 25 million fanatic players. This breakthrough triumph is popular not just with twitchy teenage boys but among people who typically never touch the stuff: women, professionals—even 40- and 50-somethings.

Maybe that’s because playing The Sims is almost exactly like coping with everyday suburban life. To play, you begin by building a home, down to the pattern of tiles on the kitchen floor and the shape of the backyard pool. You design a family to populate it and endow them with qualities like laziness or playfulness. Then, you try to help them along as they stumble through everyday life—directing them to feed themselves, keep the house warm and tidy, and remember to go to the bathroom.

Unlike nearly every other game, though, there’s no winning or losing. You're just trying to keep your Sims happy and entertained. And as Craig found out, although you may be the puppetmaster, the Sims play by their own rules. Leave a bunch of Sim teenagers unsupervised for a while as they try to make pizza? They just might burn the house down. Perhaps most eerily, your Sims have emotions: Their "happiness meter" will drop if they get hungry, or if you don't give them someone to fall in love with. Neglect them too much? They'll die.

These lifelike stakes give The Sims a genuinely existential edge, and therein lies the allure of the game. By toying with a virtual version of ordinary life, you can grapple with a very real question: What makes a person happy?

TO UNDERSTAND THE APPEAL of The Sims, it helps to understand a bit about Will Wright, the game’s creator and co-founder of the game company Maxis. The 43-year-old is widely known as the philosopher king of the computer game world, equally at home in the library as in the arcade. His games may be mass-market hits, but they’re based on some very brainy theories about behavior, economics and human psychology.

Wright's intellectual path is about as electic as possible: He attended three different colleges but never graduated, sampling courses like chocolates in a mixed box -- some computer science, architecture, mechanical engineering, even aviation. One of his early games, SimAnt, was inspired by evolutionary biologist Edward O. Wilson's famous studies of ant colonies. Wright became fascinated by Wilson’s explorations of "emergent complexity" – the idea that individual creatures operating with very simple goals can collectively produce incredibly complex behaviors. In the game, SimAnt players assemble an anthill and then marvel as it seems to grow a mind of its own. "Each ant is only doing a few simple things, but when you put tons of them together you suddenly have these really surprising results," he notes, including unusually complex ways of gathering and moving resources around. Inspired by scientist James Lovelock's "Gaia" thesis that the earth is a self-regulating mechanism, Wright created SimEarth, where players got to design and run their own planet.

When Wright began designing The Sims in the late 90s, though, he faced a more challenging task: How do you get virtual people to act the way real ones do? Ants are relatively easy to simulate, since their behavior isn't too complicated. But what are the fundamental building-blocks of human behavior?

Wright started by boning up on Abraham Maslow's Motivation and Personality, including Maslow's famous theory of the "Hierarchy of Needs". Maslow argued in the 40s and 50s that human psychology could best be explained as a quest to satisfy primal needs like hunger and safety before addressing demands such as love or self-actualization. The Sims are programmed this way, which is why they seem so human. For example, your Sim won't enjoy a movie if she’s hungry; aesthetic appreciation of a movie is a higher-order pleasure -- and she can't do it if her stomach is growling.

That means that you, the player, must learn and obey the rules that govern Sim life, many of which are hauntingly familiar. "You want to buy them a washer-dryer? Okay, but you might not have enough money left over for a phone. So what's more important, communication with your friends, or saving time cleaning?" Wright laughs. "It lays bare all these ethics of everyday life. What you shop for implies these moral choices."

The game also incorporates the ideas of economist David Friedman. In his book Hidden Order, Friedman argued that our everyday lives are a series of quasi-economic choices. In the grocery store, for example, we pick which line to stand in based on a calculus of anticipated time and hassle: "If we decide to move over to a line that seems to be moving faster, we have to give up our spot in our current line. So it's a sacrifice hoping to get something out of it," Wright notes. Modelling these little mental tradeoffs are part of how Wright gave a Sim the ability to decide between, say, sleeping late (which might make him feel more rested) or cleaning up (which might make him feel happier about his house).

In Wright’s hands, these high-browed theories have fed into a game that allows you to play out your fantasies, re-live your life, or rejigger your identity. Ever wonder what would happen if you had seven kids? Or if you were living in a huge frat house? Try it out -- set up a Sim with that lifestyle and turn it loose. In one sense, The Sims is a private laboratory to experiment with the forbidden "what ifs" of your existence. It may be the first form of high-tech self-gnosis: Mass therapy disguised as a video game.

The first thing most people do when playing the game is recreate themselves, says Wright, and they often learn something in the process. He once got a letter from the parents of an adopted Romanian boy, orphaned at age 9 or 10. The child seemed depressed--even traumatized--and wouldn't talk at all about his background. "Then they got him The Sims. And he ended up replaying his childhood in the game for them. He created a version of his family, and showed them what had happened. For him, it became a tool for self-expression."

"It gives you a model for a realistic environment," agrees Henry Jenkins, a professor of Comparative Media Studies at the Massachusetts Institute of Technology who specializes in video games. "You can program your Sim to look and sound like your last girlfriend, and figure out why your last relationship fell flat." Some psychologists say their patients actually discuss their Sims games on the couch, an updated version of the classic therapeutic technique of playing with dolls. "When the Sims works well, it's kind of like a projective test. You can really see a lot of their psyche spilling out into their games," says John Suler, a psychology professor at Rider University in Lawrenceville, NJ, who specializes in cyberculture. "I spoke to one teenager who created a version of herself and her boyfriend. Then she created another version of herself -- an evil version -- to try to steal her boyfriend. She wanted to see what it's like to be evil."

In fact, being evil may be the best part of the game. In real life, you wouldn't dream of doing nasty things to your friends and family. But in The Sims, the lid blows off your id. In hundreds of fan web-sites devoted to the game, players gleefully describe the wicked ways they've killed their Sims -- such as putting them in the pool, then removing all the ladders and waiting to see how long it takes them to drown. As in fiction and art, of course, tragedy can be powerfully cathartic. "People really love to explore 'failure states'," Wright argues. "In fact, the failure states are really much more interesting than the success states."

THE STRONGEST DRAW OF THE SIMS, THOUGH, may be its approach to modern materialism. While programming the game, Wright became intrigued by Why We Buy: The Science of Shopping, a book about the psychology of shopping by "retail anthropologist" Paco Underhill. He knew that buying stuff for your Sim household -- designer clothes or wide-screen plasma TVs -- would be a major part of self-expression, just as it is in the burbs. But Wright also wanted to do justice to the ideas of economist John Robinson, a scholar of "time studies" -- how much time the average American spends on everyday activities. Robinson discovered strange truths about our lives, like the fact that we might spend half an hour each day just getting from place to place in the house; he also found that we spend 154 minutes watching television, and 20 minutes on child care.

As in life, accumulation in The Sims also brings its discontents. As players build increasingly lavish homes, they find that it can be more of a hassle than it's worth. "Your Sim winds up spending all his time just navigating the place," Wright laughs. "Sure, you've got the pool table in the west wing -- but you've got to get there." Players buy their Sims more and more gadgets and toys, but reality bites back. "They want the dishwasher because they think it'll save them time. But if a player loads their house down too much, soon they find the stuff breaks and needs maintenance," Wright says. "Suddenly, these things you wanted so much all became time bombs, when you originally bought them as time-savers."

Nonetheless, most long-term players say designing Sim households is the chief delight of the game. "I don't really even play with the families any more. I just focus on the design. I spent a couple of days setting up a Moroccan style house, complete with a courtyard and a market," says Andrea Grimison, a 33-year-old woman in Germany who spends a few hours a day playing the game. "Now, this is a place I'd like to live in!" She set up a website to share her work, and now thousands of fans download her concepts every month.

By putting interior design at the heart of his game, Wright took a page from Christopher Alexander, an influential architect who believed that design is basic to human identity. According to Alexander, ordinary people innately grasp how environments and urban planning affect us; it's why young couples often argue heatedly over what neighborhood or city to live in. "We intuitively understand the need for privacy, or our affinity for light," Wright notes. "[Alexander] was always saying that you don't need a professional -- you can do this yourself. He became kind of the anti-architect."

While reading Alexander, Wright discovered a curious fact: Home-design software was selling millions of copies a year. Wright figured it was hardly likely that so many people were actually embarking on massive remodeling projects; in reality, they probably just wanted to play with architecture. It was part of a major shift in the zeitgeist: With the ascendancy of Martha Stewart and shows like Trading Spaces, Americans have become more sophisticated than ever about aesthetics. The Sims, Wright deduced, could be a laboratory for understanding not only our personalities, but also our personal spaces.

In the process of designing the ultimate split-level, players sometimes learn a few things about their own lives. Grimison tried creating a virtual replica of her own house. When she finished it, something weird happened: Her Sims didn't like it. "It was because my bathroom doesn't have windows, because it's in the middle of the house. And my Sims always want light in all the rooms, or they won't be happy." Lisa Anne Craig had a similar epiphany, but in reverse. "I actually used The Sims when I was painting the house. I couldn't decide what color to paint it, so I made a model of our house and I tried out various colors. Unfortunately, we picked a periwinkle. It's very Florida," she jokes, "but now I kind of hate it."

The Sims is still nothing like real life in some very important ways: there are no taxes, children never grow into adults, and there aren't any tightly-packed cities like Chicago or New York. But the virtual citizens will soon be taking another great leap toward real life. Next spring, Electronic Arts plans to launch The Sims 2. This sequel has the same basic plot, but with a few intriguing refinements: In the new game, Sims will age and die. What's more, the events of their youth will leave them with psychological baggage as they age. "If your Sims have particularly happy childhoods -- or unhappy ones -- you'll be able to see the way that's going to impact them later in life. You can see how they kind of ricochet on into the future," Wright says. He suspects it'll turn the game into an even more precise emulation of our existence ("a spreadsheet for life," as he puts it.) He's probably right. We'll play it, millions more of us, poking and prodding our virtual people to see what happens.