The rise of the idle-tap game can be traced back to Cookie Clicker, which was launched in 2013. The user clicks on cookies to earn more cookies, which can be used to buy virtual farms, banks, buildings and even grandmas who will help produce more cookies.

The game started out as a joke, its French creator Julien Thiennot has said. In a Reddit AMA he described it as “a game that no one in their right mind would play for more than 10 minutes”. The gameplay being so simple, it essentially mocked the idea of slogging one’s way through a traditional video game.

Thiennot posted his first version on 4chan. To his surprise, and the surprise of the gaming industry, it became the second-most-searched-for video game of the year. (The most-searched-for was Grand Theft Auto V, which cost millions to create and had a complex world of cars, plots and weaponry.)

Thiennot realised then, he has said, that his game had the same simple, addictive appeal of the evergreen Tetris, with fewer challenges and better rewards.

Following the success of Thiennot’s joke game, other developers launched similar games built around a range of themes. In Bitcoin Billionaire, launched in 2014, each player starts out with almost nothing: a rundown workstation, bulky computer, a desk with one missing leg, a desolate bookshelf. Start tapping to earn enough dough to swap the boxy monitor for a sleek new model, turn the crumbling office into a casino; diversify revenue streams well and players don’t even have to click to earn. Upgrades involve mansions, space and time travel.

In Dogeminer 2, launched in 2017, players start out earning “dogecoins” by beating a rock with a pickaxe, then use the currency to hire help, buy space rockets, sometimes even a time machine. Kittens can be bought to post cute videos to help earn their owner more “dogecoins”. The eventual goal is to earn enough to buy a space station and jet off on a rocket to the moon.

An apocalyptic variation called Final Fortress – Idle Survival launched in 2016 has an in-game currency called Gas. Gas can be used to expand the fortress, hire managers, upgrade each floor. The more floors a player builds, the more tools they unlock. Kill zombies to earn more Gas.

The games remain surprisingly popular. Cookie Clicker and Bitcoin Billionaire have had over 1 million downloads each on Android. AdVenture Capitalist has over 10 million. (For comparison, GTA V had sold over 100 million copies as of 2018).

As with the majority of online games, a large part of the allure comes from the false sense of accomplishment. Whether it’s Cookie Clicker, Candy Crush or Grand Theft Auto, with a few moves, one can accomplish, achieve, gain. Except, with Cookie Clicker and the other idle-tap games, a player never loses. There are no high scores except one’s own, no fixed targets, no threats. Players never have to compete. They can let their minds wander as they tap; some users say they even play while watching TV. It can, of course, become a compulsion and a compulsive waste of time.

“Idle-tap games are based on the psychological principles of behavioural conditioning,” says Dr Prerna Kohli, clinical psychologist and founder of MindTribe.in. “The rewards in these games are in much greater proportion to games of other genres. Even when the player is not playing, the games can generate rewards. This can cause an innate need to check on the earned rewards whilst inactive too, a principle similar to how a Facebook notification compels you to check the app.”

The trick is moderation, Dr Kohli adds. “When we see individuals gaming for hours every day, it can create a dependency which in turn can lead to addiction because these games cause a dopamine rush.”

While most of these games are free and earn their revenue from video ads that players can watch to earn more coins, cookies or other currency, another thing to watch out for are the in-app purchases. Between the dopamine rush and the illusion of success, one could end up with more virtual assets in one’s bank statements than one would like.

But eventually it’s not success but the promise of simplicity that draws most players. “Such games are perfect for a fast-paced life,” says Rahul Agnihotri, 32, a software developer and fan of Dogeminer 2, played once a week on his laptop, “to break away from scrolling endlessly on his phone”. “Even though you’re only tapping the screen, the goal is improvement and making things better in-game. It gets you in a positive mood very quickly. Like colouring and journaling, idle-tap games help you destress because they give you something simple to focus on.”