Pokémon GO. Whether you’ve played it or not, it’s likely you’ve got an opinion on it.

Back in July 2016, with reports of slow, shambling bodies falling into lakes, being hit by cars and generally getting into all kinds of hilarious shenanigans, it seemed that a much feared zombie apocalypse was upon us. The entertainment industry has been preparing us for years, with the likes of The Walking Dead, Zombieland, Shaun of the Dead and The Last of Us, and it was finally upon us. The thing is, there was one small yet life-saving difference with these zombies: they’re not after your brain, they’re after Pokémon.

Now that the Poké-revoltion has died down, it seems like a good time to take a look at why it became so damn popular to begin with. It may seem obvious: putting a popular franchise onto handheld devices that almost everyone owns and making it free-to-play is a sure-fire recipe for success, but I feel I owe it to you, dear reader, to break it down a little further.

First things first, full disclosure: I freaking love Pokémon. As long as we’re talking about Generation I (that’s the first 151 Pokémon, fyi) or the original anime show of the same name, then I’m your man. I even published a feature on why I believe 1996’s Pokémon Red & Blue for the Game Boy are games that changed my life.

So why did Pokémon GO become such an overnight success? Why, when the 3DS games  have moved on so far and added so many new faces, taking the total number of Pokémon now in existence to almost 800, would a mobile title with just the first 151 be so popular? (It’s now up to 248 since the addition of the Gen. II ‘mon in early 2017.)

Firstly, it’s down to the fact that the target audience of Pokémon GO is not primarily children. It’s aimed at the 20 to 30-somethings that remember playing Pokémon Red & Blue when it first came out. Nostalgia sells. For them, this game can be a doorway into the past; a reminder of simpler times when it seemed entirely plausible that, as happens in most Pokémon games, a 10 year-old kid could wander out into the world with no money to speak of and not a single Pokémon to battle with, yet end up the greatest damn Pokémon Trainer the world had ever seen. Now, they can actually become a Pokémon catcher! (I’m loathe to say Trainer because, as of now, there is no way to train your Pokémon without simply pressing the “Power Up” button.)

I get the appeal of wanting to feel like a Pokémon catcher, I do, but I think there may be a tier below that – a tier where Pokémon GO represents a bit of harmless fun and competition between friends. This is where I sit, and where most people who play the game sit. Sure, nostalgia plays a part of that, but generally speaking we love to compete, and we love the chance to be the best by managing to “catch ’em all”!

While it may be aimed at adults who grew up playing Pokémon, the game of course still appeals to children, too. Pokémon is just as relevant now as it was 20 years ago, and while the youngest generation of players might not have a smartphone of their own to play with, Pokémon hunting has become a hugely popular family activity. Parents who previously might not have been interested in video games are suddenly out with their children, hunting for imaginary creatures. And often, they’re enjoying it just as much as the kids.

Of course, the fact that Pokémon GO is seen as pure, harmless fun is a massive factor. For me, it was neat seeing a cute little Charmander standing on the street in front of me, or a Zubat flapping away in the corner of my office, and I really enjoyed the forced perspective that made a simple Krabby and an effortlessly majestic MagiKarp appear like titans in baseball stadiums.

For others, augmented reality carries a novelty factor that’s hard to overlook. If you’re a cynical old git like me, you probably think, “What’s so special about some augmented reality?” but even I can’t deny just how far the technology has come in recent years.

It’s not just the technology or its novelty factor that holds the key to Pokémon GO‘s success though. As humans, we’re hardwired to be drawn to collecting things. Our “hunter gatherer” instinct has been exploited by video game makers for years – like when Call of Duty gives you a new gun and a little musical melody for levelling up, or how Fifa now has the “Ultimate Team” where you can pay to collect better, shinier cards than your friends. Pokémon GO exploits it too by not only having hundreds of creatures to strive to collect, but also by placing Pokéstops around the world to give out trinkets when you pass. You’ll want to have more – and better – equipment and Pokémon than your friends, so you catch more critters and collect more kit. It’s addictive – and if you are so inclined, expensive.

When you get to around level 18, the amount of XP you need to increase each level begins to reach agonising levels, meaning it becomes a bit of a grind to level up. It becomes more of a pain, though by this point you’ve likely invested so much time (and possibly money) that you won’t want to stop now. You’re going to have 80-90 Pokémon in the Pokédex, so you may as well keep playing, right? That’s what you’ll tell yourself. Now we’re beginning to see why Pokémon GO became so popular: it’s as addictive as Rare Candy!

All this considered, then: just what’s the point of Pokémon GO? When you’ve collected your Pokémon and powered them all up, what can you actually do? That’s an easy one: become a gym leader. Once a gym has been won – or if you’re lucky, simply found with no team in control of it – you can place one of your Pokémon in there to claim it for yourself and then defend it from attackers. It’s another addictive element of the game. Capturing a gym and becoming the leader feels good; if that gym has been lost by the time you next see it, you’ll want to reclaim it. Even better, if a friend is a member of a different faction, you can battle each other to see who’s the best, or if you’re on the same team, put both your most powerful Pokémon in the gym and see how long they last.

Maybe its addictiveness is what’s responsible for Pokémon GO‘s ultimate success, or maybe it’s the nostalgia, the bright colours or the competitive elements. Or perhaps, just perhaps, it’s the rare combination of all of these things that wrote developer Niantic’s runaway success story. We may never know for certain.