The willing suspension of disbelief was Samuel Taylor Coleridge’s description of the interaction between readers and writing. In general, readers have to suspend their knowledge that they’re reading fiction. They have to enter into a kind of agreement with the writer to withhold any innate skepticism and allow the author to make her case.

It’s easy to see how this idea works out in fantasy. The reader agrees to accept a world in which vampires or werewolves exist. In turn, the writer agrees to provide a world in which these creatures can function. Win/win, right?

But what about works that aren’t fantasy. Do happy endings require willing suspension of disbelief? Sometimes. Particularly if either the hero or heroine has character flaws that make you doubt their ability to function in the long term. But if you like the characters, you’re usually willing to overlook their problems and hope for the best.

To me, the more troubling situation comes when the author has created a premise that requires the reader to ignore some basic realities. I ran into that situation lately in a suspense thriller.

Now thrillers have their own set of standard premises. For example, you frequently have to accept the idea that there are lots of serial killers out there, and that they’re all fiendishly clever in the tradition of Hannibal Lector. If the author is skillful enough (e.g., Tess Gerritsen), you’re willing to overlook the unlikeliness of this situation and allow her to weave her plot without asking uncomfortable questions. The problem comes when those questions intrude anyway. The thriller I was reading depended on the idea that a brilliant psychiatrist was setting up a special prison-and-treatment-center for psychopaths. She was collecting these psychopaths from prisons around the country and building her center in a remote corner of the US to enable a corps of psychiatric professionals to perform long-range studies.

I was ready to buy in at first. Until the psychiatrist heroine arrived at a prison to interview one of her potential subjects. But then I found myself thinking “Are these state prisoners?” Which led to, “How is she able to take care of all the various jurisdictions?” Other objections began to occur to me. Were there really that many violent psychopathic killers who weren’t on death row? Given that traditional psychiatry has been under attack for a while, how many states would really buy into an idea like that? And, most of all, where the hell would the funding come from?

At that point, of course, I was way outside the story. And the fact that the heroine was being stalked by, you guessed it, a psychopathic serial killer was another problem.

And that’s the real risk with the willing suspension of disbelief. Once you lose it, it’s hard to get it back. I found it difficult, if not impossible, to crawl back into the story and let the author get on with it.

Most popular fiction is based on premises outside reality, and much of the time readers are willing to buy in. But if one little crack shows up in the world the author is building, the result may be total collapse. After all, you’re asking your readers for faith. And faith requires a strong foundation.