Excerpted with permission from Riveted: The Science of Why Jokes Make Us Laugh, Movies Make Us Cry and Religion Makes Us Feel One with the Universe, by Jim Davies. Available from Palgrave Macmillan Trade. Copyright © 2014. (Scientific American and Palgrave Macmillan are part of Holtzbrinck Publishing Group.)

We know that parts of our minds think scary stories are important because our minds find them important enough to dream about. If scary stories are important, then we are compelled to experience them. “Please watch The Terminator again,” our lizard brain says, “I need to brush up on how to deal with killer robots from the future.” At the same time, many stories, even harrowing ones, feature happy endings. Danger is more valuable to watch if combined with a way to escape it. There are cultural differences in how stories tend to end. American plays (as of 1927, anyway) feature happy endings more often than those of other cultures, such as Germany’s in spite of some regional differences, however, my theory predicts that, worldwide, stories that can be classified as having happy endings will be more common than stories that can be classified as having unhappy endings.

Some things are compelling in a way that makes us passionate, or give us pleasure. Others are compelling in an addictive, obsessive way: we don’t really get a whole lot of pleasure from the activity, but we don’t want to stop, either. Experts debate what kinds of things one can become addicted to in a medical sense, but I’m using the term casually, where it can be a positive description of a food or activity that we find so rewarding that we can’t help but continue to partake, such as being addicted to potato chips or to a television show, or playing Tetris.

I’m not aware of any scientific research on the subject of what makes a computer game addictive, but I will speculate that we get addicted to games and puzzles because we feel we are getting better at something. Getting better at something makes us feel good about ourselves, fitting into the theme of hope in this chapter.

Grinding is a computer-game term for a situation in which a player must repeat actions over and over again for some kind of (usually in-game) reward. For example, a player might have his character kill monsters, over and over again, to gain powers or status. For some games, grinding is perceived as essential, because meaningful content is expensive to create and consumed far more rapidly by gamers than can be created by game designers. It’s hard to make grinding fun, but game designers have found clever ways to make grinding addictive. One way to do this is to give a very small reward for each action. In the Lego Star Wars games, nearly every action gives some kind of reward. The player feels that he is constantly making some progress, however small. The external reward in the game is matched with an internal reward in the gamer’s mind. Often this mechanical reward (e.g., experience points or virtual gold pieces) is accompanied by an intrinsically rewarding stimulus, such as a bright icon and a pleasant sound.

Slot machines are computer games that work by grinding. The player does a very simple action—pulling a lever—over and over again, in hope of financial reward. Unlike Lego Star Wars, however, slot machines do not reward every time. Shouldn’t they be less addictive?

Actually, no. It turns out that intermittent reward reinforces behavior even more strongly than reliable reward. Some games take advantage of this by rewarding the player at random intervals. In many computer games, for example, X-Men: Legends, the player can destroy boxes, but the boxes only occasionally reveal valuables. This encourages the player to addictively destroy every box she sees. Slot machines have another insidious aspect to them—one can feel like one is getting better at them. To understand this, let’s take a familiar example of a child trying to hit a tree with a thrown rock. When the kid throws a rock and it hits the tree, she gets a surge of positive feeling. This is the brain’s internal reward system. It rewards all of the ways her muscles moved, so that in the future she will be more likely to hit the tree again. However, if she fails to hit the tree but comes close to hitting it, there is still reward, albeit not as much. She perceives that she is getting closer to the target, getting better at the task. More like that, the brain says. It feels pretty good to almost hit the tree.

The same thing happens to her when she is an adult using a slot machine, even though in the slot machine case this behavior is irrational. When she gets two “bar” results but not the third, she feels (subconsciously, of course) that she got “close” to the desired result. Her brain assumes she is getting better at the task, so there is a self-generated reward, as Catharine Winstanley found in a brain study. It feels good to get close, even in a slot machine. It is completely irrational because the slots are random, getting two “bar” results is not really “close” to getting three, and of course how one pulls the bar has no effect whatsoever on the outcome of the machine. It’s completely different from throwing a rock at a tree, but our minds cannot make this distinction.

The vast majority of people at Gamblers Anonymous meetings are not addicted to tabletop blackjack or the roulette wheel—they are addicted to machines. Slot machines and video poker are computer games that take your money even more quickly than the prototypical computer games people think of when they hear the term. What is even worse is that unlike most computer games, casino slot machines collect an incredible amount of data on how the design of their games affects how much money is made. As a result, these gambling computer games are probably the most addictive artifacts ever designed.

The world experts at catering to our hopes and fears are the news media, who created the phrase “if it bleeds, it leads.” They now that terrifying stories will get them attention, so they end up reporting as many of them as they can.

Sometimes the news will cleverly play on our hopes and fears one after the other, with a headline or teaser like “is your child being mistreated in preschool? Find out what you need to know.” Like religion, the news scares you and follows up with hope for a solution.

Sometimes the news caters only to hope. No doubt many readers have heard that having a pet increases happiness and health. But few know that the studies reporting no effect are just as numerous. A study showing no such effect is something nobody wants to read. It’s not scary nor hopeful enough to grab anyone’s attention. It’s in the boring dead zone, the anti–sweet spot. As a result, in this case only the positive gets reported.

Like a lot of news, contemporary legends (popularly known as urban legends) tend to be scary. That is because the scary ones are more likely to be retold, as was found in an experiment by psychologists Jean Fox Tree and Mary Susan Weldon. According to my theory, we find cautionary tales compelling because of fear and hope.