Some of this research starts with a fundamental question: Why do people like stories in the first place? As Yale psychology professor Paul Bloom points out in his book How Pleasure Works, it's puzzling that we spend more of our free time exploring fictional worlds—reading, watching TV and movies, playing video games—than engaging in real-world pastimes. "Surely we would be better off pursuing more adaptive activities—eating and drinking and fornicating, establishing relationships, building shelter, and teaching our children," he writes.

So what's with our obsession with make-believe? Bloom and others argue that, on some level, we don't distinguish fact from fiction. There's research to back this up: For example, a study found that people refuse to eat a piece of fudge shaped to look like feces, even though they know it's just fudge. Appearance and reality get blurred. We like stories about sex because we like having sex, and somewhere in our minds, the two are the same. As Thalia Goldstein, a psychology professor at Pace University, explained to me, this blurring actually happens at the neurological level: The conscious, thinking parts of our brain tell us that a story isn't real, but the more primitive parts tell us it is.

This research suggests one explanation for why spoilers suck: They remind us that a story is just a story. It's hard to get transported when you already know where you'll end up—in real life you don't have that knowledge.

Of course, not everyone shares my spoiler hatred. A recent study found that people who heard the "spoiled" version of a short story liked it more than those who heard the "unspoiled" version. But as Goldstein pointed out, the study overlooked a key fact: People only care about spoilers for stories they feel invested in, not those they've heard for the first time a minute earlier.

Some spoiler defenders make more theoretical arguments, such as Time's TV critic James Poniewozik, who wrote, "An unwanted spoiler does take something away, but not, I think, the pleasure of actually reading or watching a story. Rather, it takes away from the anticipation before watching it—wondering who dies, whether they'll get off the Island."

But taking away the anticipation does take away the pleasure of a story. There's plenty of research showing that people enjoy the anticipation of something pleasurable as much as—or sometimes even more than—they enjoy the thing itself. That's why a study found that people would rather postpone a free dinner at a French restaurant by a week than have it right away; they want the pleasure of looking forward to the meal. As Harvard psychology professor Daniel Gilbert says in his book Stumbling on Happiness, "Forestalling pleasure is an inventive technique for getting double the juice from half the fruit."