A year after the game's mobile launch, we still can't stop playing. The app's designer and psychology experts weigh in on exactly what makes it so irresistible

TIME illustration / Hands: Getty Images

If you haven’t heard of Candy Crush, it’s the mobile game that’s so addictive, players say they have left their children stranded at school, abandoned housework and even injured themselves as they try to reach new levels of the game.

Candy Crush has been played 151 billion times since it launched as an app on mobile devices exactly year ago. And it’s the first game to ever be No. 1 on iOS, Android and Facebook at the same time. Candy Crush’s creator, King, a Stockholm-based company, says 1 in every 23 Facebook users plays it. And while Candy Crush is free, the in-game purchases that some players choose to make add up. Think Gaming, which releases gaming analytics, estimates that it takes in $875,382 per day. (By comparison, another insanely popular mobile game, Angry Birds, takes in an estimated $6,381 daily.)

(MORE: Quiz: How Addicted Are You to Candy Crush?)

All that adds up to some seriously distracted users. A survey by Ask Your Target Market polled 1,000 players and found that 32% of them ignored friends or family to play the game, 28% played during work, 10% got into arguments with significant others over how long they played, and 30% said they were “addicted.”

But there are lots of amusing games out there, so what’s so addictive about this one?

We asked Tommy Palm, one of the game’s designers, what the King team did to get us hooked. We also called a few psychology experts and players to understand the backstory on why their tactics worked so well. Here are the nine reasons they say Candy Crush is so irresistible:

1. It Makes You Wait

Perhaps the most genius element of Candy Crush is its ability to make you long for it. You get five chances (lives) to line up the requisite number of candy icons. Once you run out of lives, you have to wait in 30-minute increments to continue play. Or, if you’re impatient, you can pay to get back in the game — which is why it’s bringing in so much revenue. “You can’t just play all the time. You run out of lives,” says Andy Jarc, 22, one of the few players to reach level 440 in the game. “So the fact that they kind of constrain you — the whole mantra, ‘You always want what you can’t have.’ I can’t have more lives and I want them.”

“I think it makes the game more fun long term,” says designer Palm. “If you have a game that consumes a lot of mental bandwidth, you will continue playing it without noticing that you’re hungry or need to go to the bathroom. But then you binge and eventually you stop playing. It’s much better from an entertainment point of view to create a more balanced experience where you have natural breaks.”

2. We’re All Suckers for Sweet Talk

You flick four candies in a row, and they zap away. Candies above begin to cascade down, making even more matches. At the end words pop up on your screen, accompanied by a voice that says “Sweet” or “Delicious.” This feedback is essential for player immersion. “Positive rewards are the main reason people become addicted to things,” says Dr. Kimberly Young, a pioneering expert on Internet and gaming addiction who treats those addicted to the cyberworld. “When you play the game, you feel better about yourself.”

3. You Can Play With One Hand

According to Palm, the icons and setup were created so players could multitask. You can play Candy Crush while carrying a drink, toting a purse or bag, clinging to a subway pole, or hiding your phone under the table. That’s a huge advantage and makes this game perfect for a train ride, a distraction while you’re waiting to see a doctor, or something to get you through boring meetings. Plus, you can play offline as well — so even if you’re stuck in a tunnel, you can be “crushing.”

4. There’s Always More

According to Palm, the Candy Crush team updates the game constantly and creates new levels every two weeks. Right now there are 544 levels. “Just three years ago, a game with 30 levels would be astonishing,” King says. “And now with this game, it has raised the bar with how much content a mobile game should and will have.”

Plus, on any single level, there’s no way to fail. If you run out of options on a board — and that happens once in a blue moon — the board immediately resets. You never get stuck. You can’t lose. “I believe this is part of the reinforcing pattern which keeps you playing,” says Dr. Dinah Miller, a psychiatrist who has written about the addicting elements of another popular game, Angry Birds. The game only ends when you’ve run out of your allotted number of moves “and you can end that frustration by buying your way out.”

5. You Don’t Have to Pay – but if You Want to, It’s Easy

King reports that of all the players on its last level — 544 — more than 60% of them didn’t pay a cent to buy extra lives or chances to get there. But if you want to pay, it’s easy. Connected to Facebook or the app store? Just click to pay.

6. It Taps Into Our Inner Child

“Many people have had a very positive feeling about candy since they were kids,” says Palm. “And it makes for a really nice visual game board with a lot of color and interesting shapes.” In fact, when you play you feel as if you’re transported into an entire Candy Land experience. The game pieces are candy, and the homepage for the game looks like the traditional Candy Land board, with your Facebook friends’ pictures displayed as pieces on that board, sitting at whatever level they’re stuck on.

7. It’s Social

Social games — any game that allows you to connect with your friends through a social-media platform like Facebook — have taken off. Whether it’s Words With Friends, Kingdoms of Camelot or Candy Crush, the ability to play with, or compete against, friends is irresistible. “Look, nobody’s coming to me because they have a clinical addiction to Candy Crush,” says Young. “It’s more of a social addiction, if you will.”

8. It’s an Escape

“When you read the research about gaming,” Young says, “you’re often looking at people who are distracting themselves from something in their lives.” The relaxing exercise of lining up candies to the tune of upbeat music is a perfect stress reliever.

9. It Grows on You

This isn’t your average “line up three” game. “I started playing, and at first I was like whatever, it’s just bejeweled,” says Jarc. “But as I played more and more, it became addicting.”

King’s high-level of attentiveness toward updating gameplay has made it better quality than most casual games that are out there. When players took to Facebook to express their frustration with level 65 — notoriously one of the hardest levels in the game — King went into the game and altered the level to make it easier (though not too easy) multiple times.

Update 10:11 a.m.: This post has been updated to reflect that Dr. Dinah Miller is a psychiatrist, not a psychologist.