For parents of children who are interested in video games, it can be difficult to understand what makes one game harmful and another benign. How do you know whether to buy a game for your child?

The Entertainment Software Rating Board (ESRB) rates most mainstream games on a system from Early (EC) to Adults Only (AO). It is similar to the ratings given movies; a game rated “Mature” is roughly equivalent to a movie rated “R.” This is a good indicator of the content of the games, but not the mechanics. For example, Candy Crush contains no violence, sexual content, or inappropriate language, but it is highly addictive; there are reports of people playing the game instead of spending time with friends and family and neglecting to pick up their children from school.

Many parents feel helpless, for good reason. Games have changed in the decades since Pacman was released, and it’s hard to keep up. Game creators are getting better every day at making their games more enticing, more immersive, and harder to put down.

Here are a few factors to look out for.

“Free to Play”

Many games use a “Free to Play” model, which allows them to amass a sizable following quickly. Because one can play the game for free, there is no obvious downside to trying it. Most games in this category start with a tutorial which introduces all of the concepts. They are then instructed to perform several simple tasks, all rewarded with colorful graphics and positive messages.

For example, after completing the first level of Toon Blast, a game in which players tap groups of colorful squares in a grid, the game proclaims “Toon Blast!” and fireworks replace several of the squares, which detonate and give thousands of extra points. Immediately afterward, the screen dims as more fireworks explode in colorful showers, confetti rains, “Level Completed!” pops up, and three elated cartoon characters jump into the air wearing party hats. Then, the game shows the player that they’ve earned three stars (animated and shiny) on that level and immediately begins the next one. This structure is typical because game designers know that players crave this sort of reward.

Once the player is interested, the game becomes increasingly difficult, but it offers ways to augment play by paying a few dollars for extra chances to try a level or by removing barriers from the game’s mechanics. These are detailed below.

Waiting to play

Many free-to-play games earn money by forcing players to wait to complete actions—unless they pay to skip this delay.

For example, a game might give a player enough stone to construct a small mining camp, which will produce more stone over time. After several buildings are built for free, the player might have to wait for 10 seconds while they save up resources to create another one. After that, it might take 60 seconds to get enough. Then five minutes. Then an hour. After reaching high levels in some games, this wait might extend to a week or more.

Other games allow players a certain number of attempts at a level by giving them a number of “lives” to use. Once those lives are spent, they are “recharged” over time, often at a rate of one life per hour.

It seems counter-intuitive that a game would make a player wait to continue playing, but this wait serves two purposes. It requires the player to keep opening the app, which itself becomes a habit. More importantly, it is an effective way to earn money from players. Games like these offer a way to skip the wait by paying with in-game currency. Once the amount the player starts with runs out, there is no easy way to replenish the currency except by paying with real money.

Moving goalposts

World of Warcraft is often considered one of the industry’s most addictive games, with good reason. It is immersive, fun, social, and nearly impossible to win.

Even if players were able to finish all of the objectives, the creators release a massive expansion of the game every two years. New quests and areas help keep the game interesting, but they also deny players any sense of completion.

Neat endings help people gauge when to stop doing any activity. It’s hard to stop browsing Facebook partly because of the “infinite scroll” feature, in which users can never reach the bottom of the page. If there were an obvious end, people would stop scrolling when they got there. It’s part of the reason so few people go to the second page of Google searches.

If players could “catch up” and complete all of the available content, many would stop playing.

Progress bars

Many modern games come with a visual representation of how close one is to completing an objective, called a “progress bar.” These are usually a horizontal rectangle which slowly fills in as one gets closer to an accomplishment.

For example, in the game Skyrim, in which players navigate a world, their in-game skills become more powerful when used repeatedly. For example, after a player uses a sword a set number of times, their skill with that sword increases. Players are provided a progress bar to display how close they are to reaching the next level.

When one is close to leveling up a skill, it is easy to justify playing for a few more minutes to reach the next level before quitting. As previously mentioned, it is easiest to stop playing when a goal has been reached.

When players are given several bars which fill at different rates, it forms a subtle trap; there is always a bar that is almost full. A player might notice that their skill with a bow is close to increasing, so they decide to go to sleep as soon as it does. But as soon as it levels up, their ability to cast spells is almost ready to level up, so they decide to play until it does. As soon as that fills, their ability to block attacks is almost full. It’s a potentially endless cycle.

Playing with friends

The ability to share a gaming experience with others is a great way to make and maintain friendships, especially for shy people. It’s often easier to talk while doing something together. However, gaming with others does come with certain risks.

When one is on a team in any environment, it comes with certain expectations; people commit to spending time and energy supporting everyone else. In most cases, this is a positive experience; being on a team is a natural way to meet others and build relationships. However, it can quickly become a problem. When a child has peers who are counting on him, it can be hard to tell them that he wants to do homework or go to sleep instead of playing another round.

Case study: Fortnite

Fortnite is currently one of the most popular video games in the world. Almost all of my clients play it, and the most common concern I hear from parents is that their children play too much.

Clearly, the game has managed to do something for its fans that keeps them playing. What is it?

Wait to Play: Fortnite does not make players wait to play or use an energy system. This is part of the game’s appeal; people can play the game as often as they’d like for as long as they want.

Moving Goalposts: Every few months, a new “season” of the game starts. Everyone’s progress is reset and a new set of rewards is introduced. The rewards are earned by playing the game and completing challenges. New challenges are added weekly and include tasks like dealing “500 points of damage using explosive weapons.”

These rewards are cosmetic, which means that they do not enhance your character’s skills or give you an advantage; they purely make characters look cooler, funnier, or more unique to other players. These cosmetic upgrades are kept across seasons, so players can customize their characters using a combination of upgrades previously unlocked.

Progress Bars: The aforementioned challenges and experience points are tracked using progress bars.

Playing with Friends: This is the element which has the biggest impact on players. Parents often complain that their children do not stop playing when asked. The reality is that from the players’ perspective, they simply can’t. Because they are playing with other people, they cannot pause the game. A player’s character might die in the first minute or two, but also might survive for the full 20-30 minute round. Additionally, because players have the ability to play on a small team with their friends, leaving in the middle of a round might cause all of their friends to lose. For many young people, this is simply not an option.

What should parents do?

It can be helpful for parents who are concerned about their children’s use of video games to try the games themselves. Checking to see which of these mechanics exist in the game can help to decide whether a game may be problematic for young people who have trouble balancing the of video games with the rest of their lives.