It took six weeks for the masses to obsess over and then just as quickly get over Draw Something. Just a month after Dots stole away our attention, Candy Crush swooped in to occupy our idle time. Now, less than four weeks later, doesn't it seem like people are already getting over that, too? You know when Newsweek and The New York Times start writing about a trend it's the beginning of the end. (And, just as the company is preparing itself for an IPO, too!) Along with our shrinking attention spans for everything else in "modern life," we even have also developed a low tolerance for our leisure activities, a tolerance that seems to be getting lower and lower. 

The phenomenon fits in with the general panic over what the Internet and technology are doing to our brains. But there's something particular about phone games that make them so easy to cycle through. Social networks have their moments, but almost 10 years later and people still use it on their phones. Games—at least ones of a particular sort—on the other hand, have an ever-shrinking life span. 

Our short-term interest in popular phone games has a lot to do with their design. These are "casual" games, meant to grab the attention of the masses—rather than of dedicated gamers. To attract that audience means creating a world with a very low barrier to entry. That not only means a simple mechanism—like connecting the dots—but often it results in something familiar, as game maker Blue Key Red Key explains:

This core gameplay mechanic instantly clicks with you because it resonates with something you already know from the real world. Whether it is the logic behind catapults as in Angry Birds, the logic behind rope cutting as in Cut the Rope or the slicing of fruit as in Fruit Ninja, the relationship between what you do, and what plays out on the screen seems intuitive and logical. 

These games have to be simple because they fill a very specific niche in our lives: We play them during bite-sized moments of free time—waiting in the checkout line, sitting at a bar before a friend comes, etc. Complexity would make it a different kind of game for a different kind of gamer. 

Of course, that design also cuts down on the staying power of these games: If they're too simple they get boring. Despite having tons of levels or variations, it gets old, fast—which is one reason we lose interest in these games in the first place. For some period of time it's really fun to play one more dots game to get that high score, but then all of a sudden it's not. Look back at the downfall of Draw Something or Bejeweled and that's exactly why their users fled.

Game makers understand this and have now started to build in more variation not only to pull people away from one game to another, but hoping to hook users longer. Candy Crush, for example, tweaked the idea behind Bejeweled adding different goals for certain boards, making it "the absolute, diabolically perfect mix of tormenting addiction and genuine fun." One would think this would increase the shelf life of a game. But, that's not how evolution works in the digital age: As the game adapts, so does the user. You see it in memes and Twitter jokes and Internet headlines: The bar for success keeps getting higher, and yet the shelf life continually decreases

The same goes for these games: Dots was simple and beautiful and perfect, until Candy Crush came along with a slightly more complex offering. But now that we know it can get better, we're already ready for the next best thing. This race to the bottom explains why failing time-wasting game-maker Zynga is shifting away from casual gaming to "midcore" games, which "blend the depth of hardcore games, traditionally played on a PC or console, with the approachability and accessibility of casual games that are mobile, free-to-play and social," says Steve Parkis, senior vice president of games, at Zynga. It's a losing battle for our attention.