Have you got the fever? Oh yeah you've got the fever. Pokémon Go is here, and you are feelin' it. Charizard? Char-was-easy. Grimer? Get the Muk in my Pokéball. Doduo? More like do-duon't waste my time. Gotta catch 'em all!

The mobile game was released in the US on July 5, and it is already one of the top downloaded apps in both Android and iPhone stores. Though Niantic1 has not released official numbers, TechCrunch reported on July 11 that Pokémon Go has been downloaded 7.5 million times since its debut. And SimilarWeb's analytics shows that the game's users are logging an average of 43 minutes each day. Simply put, Americans are obsessed.

Which is not totally surprising. Pokémon Go is a video game, video games are fun, people like to do fun things. But Pokémon is different. The franchise is 20 years old, with a dedicated fan base. Pokémon Go adds a layer of real world interactivity to the game's already successful formula.

People play video games for different reasons. You like RPGs, while your sister is gung-ho for first-person shooters. "There has been some research around motivation to play games and what kinds of things that different types of people find engaging and motivating," says Jamie Madigan, psychologist and author of PsychologyofGames.com. Quantic Foundry, a game analytics consultancy, has broken these down into six core motivations: action, social experiences, mastery, immersion, creativity, and achievement experiences.

Dwell on that last one for a second. Video game achievements like trophies, awards, or levels don't earn you anything in real life. And yet these brownie points are how many games build player loyalty. A 2015 study published in the journal Computers in Human Behavior found that a group of users was way more likely to engage with an app that had "trophies" than the same app without.

The draw of those achievements is strong. The addiction of leveling up is a big reason World of Warcraft is so popular. In game achievements are such powerful motivators that they have been outsourced to other, non-game apps: Gamification is why you feel good when your fitness tracker buzzes your wrist every 10,000 steps.

The achievement experience is the core game mechanism for the entire Pokémon franchise. Think about it. "You get more Pokémon so you can not only fill in your Pokédex, but also so you can get resources to train and level up what you already have," says Madigan.

That could describe any Pokémon game. Pokémon Go is unique (and perhaps uniquely addictive) because it interfaces with the real world. Augmented reality could be a gimmick, or it could be the key to a whole new market of games. But if the latter turns out to be true, Pokémon Go could change the way we walk around.

Human beings have a long history of being obsessed with achieving things while they are walking around. And I'm not just talking about parkour. Have any friends who are into birdwatching? Frisbee golf? Catching insects?2

Or perhaps geocaching is the best analogy. Forget about what you see on your phone after it buzzes. Because getting to see some animated monster overlaid on a city sidewalk is not why you are running across four lanes of traffic to bag the Mewtwo across the street. The real augmented reality is not what you see on your screen, but what you feel in your pocket. Pokémon Go is linked to your GPS, and when you pass near a Pokémon, gym, or pokéstop, it gives you a little buzz. "You're then rewarded by a new Pokémon or some items," says Madigan. "It's very basic psychological conditioning."

Which is disconcerting, but maybe you could use an excuse to get up and go for a walk.

1Update 7/13/16 16:00 ET: This post has been updated to clarify that Niantic and The Pokémon Company are separate businesses.

2Pokémon's creator, Satoshi Tajiri, was inspired by his childhood hobby of collecting and cataloguing insects.