Most readers here already know the definition of a spoiler as it relates to stories. For those that don't, a "spoiler" is a piece of information about an event that will occur in an upcoming episode or issue or book. Spoilers are usually available online, but they can occur in casual conversation as well. Sometimes it's by accident; someone lets something slip without meaning to. Sometimes it's on purpose, either information provided discreetly beyond a link solely for those who want to be in the know, and sometimes the information is deliberately put out in plain view due to carelessness or for less innocent reasons. There's some debate on what constitutes a spoiler -- for example, is casting considered too much information?

But this isn't about what kinds of details should be considered "spoilers," or whether spoilers are good or bad. This is about what effect spoilers have on the viewer. How does knowing what's going to happen in advance change how we respond to a story?

A large part of storytelling is suspense, the not knowing what's going to happen next. But it's ridiculously easy right now to know a whole lot about what's going to happen next. Just for starters, there are websites such as http://www.spoilerfix.com (hey, don't blame me if you click through!), with tidbits on upcoming arcs on a number of TV series. Movie trailers seem to give away some of the best one-liners and major plot points, in addition to showing off many of a film's big money-shot visuals. For comic books, there are previews, scans of the cover or select pages. The final installment in a certain popular series of books which shall not be named has rumors flying from end of the internet to the other.

Being in the know about what's going to happen next is widespread, although it seems there are equal numbers who manage to avoid any advance details. Judging by how people react to finally seeing or reading that installment, however, the enjoyment is no less for those who knew the big twist. The only difference is personal preference. For some, knowing the twist ahead of time doesn't do anything to diminish the adrenaline rush of surprise. For others, knowing in advance creates problems.

Knowing what's going to happen increases the enjoyment for some people, as much as being completely shocked does for others. If a plot twist is unpleasant, or involves a character acting in a way fans won't be happy about, being spoiled ahead of time can help soften the blow and maybe those who knew won't be as unhappy as those who were unprepared. Knowing in advance, while it creates more room for anticipation, can also create more room for worry. The viewer makes decisions about the story before actually seeing it play out.

Being spoiled brings with it the slow build-up of anticipation, having time to relish and think about an upcoming moment, imagine how it might go. While it seems as if being completely unprepared would be most likely lead to the jolt of surprise, that jolt can happen even if the viewer does know what's going to happen. Why else would we buy our favorite series on DVD to rewatch them? Why do we still jump at the scariest parts of a favorite horror movie? It's like the brain goes into story mode and we forget that we've seen it before or knew what was coming, caught up in the emotion and suspense of that moment.

Maybe it's like mental muscle-memory, an echo of the emotion we felt the first time we learned the big reveal. If so, that doesn't explain how those who are spoiled, or who have already watched, still momentarily worry for the characters' fates, even if they know the heroes will be just fine in the end. A root of story lies in suspense, in not knowing what's going to happen next. Yet stories continue to thrive in this age of spoilers and inside information.