It seems like the obvious way to start an article about spoilers is to spill the beans about how it'll end. But if we're going to do that, then we must adhere to current convention and slap the words "spoiler alert" in front. Also following convention, we'll write the phrase like this: SPOILER ALERT; or like this: spoiler alert!; or like this: **SPOILER ALERT** just in case. This fully alerts you, the reader, to the probability that in the following paragraph you'll learn the major twist in the argument put forth, making it entirely possible that you'll have no interest in reading further.
Having read those fateful words, you're on your own. The article and its author are off the hook, hands fully washed of all responsibility for ruining your reading experience. If you choose to read on, the flavor of anticipation could suddenly go stale, the page might darken before your eyes and you'll possibly find your attention wandering to other HowStuffWorks topics.
On the other hand, the spoiler might have the opposite effect. Say, for instance, that you read the following (SPOILER ALERT!): "Studies indicate it's possible that spoilers aren't as rotten as you think." Now the urge to continue reading the article stems from a desire to know not what it's going to say but how it's going to say it.
It could be argued that, in this case, the spoiler has morphed into a sophisticated form of "teaser." But it's not. By accident or design, a spoiler can spoil because it forks over vital information a little too early. A teaser is designed to entice you, to whet your appetite for information, to seduce you into reading further. A teaser would read, "Do spoilers really spoil?" And the answer would be: Maybe they do, maybe they don't. To find out, you'll have to read on.