For a while, their message was everywhere. They paid for billboards, took out full-page ads in newspapers, distributed thousands of tracts. They drove across the county in RVs emblazoned with verses from the books of Revelation and Daniel. They marched around Manhattan holding signs. They broadcasted day and night on their network of radio stations. They warned the world.

That warning turned out to be a false alarm. No giant earthquake rippled across the surface of the earth, nor were any believers caught up in the clouds. Harold Camping, the octogenarian whose nightly Bible call-in show fomented doomsday mania, suffered a stroke soon afterward and mostly disappeared from sight. The press coverage, which had been intense in the weeks leading up to May 21, 2011, dwindled to nothing. The story, as far as most people were concerned, was over.

But I wanted to know what happens next. If you’re absolutely sure the world is going to end on a specific day, and it doesn’t, what do you do? How do you explain it to yourself? What happens to your faith in God? Can you just scrape the bumper stickers off your car, throw away the t-shirts, and move on?

In order to find out, I got to know a dozen or so believers prior to the scheduled apocalypse. I sat at their kitchen tables, attended their meetings, tagged along on trips to Wal-Mart, ate pizza in their hotel rooms, spent hours with them on the phone. Then, after Jesus was a no-show, I stayed in contact with them—the ones who would talk to me, anyway—over the following days and months, checking back in to see how or if their thinking had changed.

I learned a lot about the seductive power of radical belief, the inscrutable vagaries of biblical interpretation, and how our minds can shape reality to fit a narrative. I also learned that you don’t have to be nuts to believe something crazy.

“I Can’t Afford to Doubt”

On the night of October 22, 1844, they huddled in a barn in Port Gibson, New York. They stood by the graves of their departed loved ones in Sugar Hill, New Hampshire. In Cincinnati, Ohio, 2,000 of them walked through downtown and climbed a hill to a park overlooking the city. Inside homes, on rooftops, in fields, alone or en masse, they waited for God.

These were devotees of William Miller, the prosperous farmer turned self-taught biblical scholar. It’s impossible to know for sure how many people he persuaded that the world was ending; estimates range from 50,000 to one million. Anyone who read a newspaper at the time would have been familiar with Miller’s prognostications. Along with those who identified publicly as Millerites, there must have been many more who privately took his warnings to heart.

More than a century later, a young social psychologist named Leon Festinger took an interest in the Millerites. What intrigued Festinger was why the failure of Miller’s multiple prophecies had done little to discourage the faithful. Miller had predicted the end of the world more than once. The end of the world hadn’t come. Shouldn’t that have been enough? Festinger wrote the following in his 1956 classic, When Prophecy Fails: “Although there is a limit beyond which belief will not withstand disconfirmation, it is clear that the introduction of contrary evidence can serve to increase the conviction and enthusiasm of a believer.”

When the world failed to end, they clung more tightly to their belief. Rather than folding, they doubled down.

Festinger wanted to understand this phenomenon. The Millerites were long gone so instead he focused on Dorothy Martin, a suburban homemaker who believed that she was able to communicate telepathically with superior beings from the planet Clarion. They told her things and she wrote down what they said. One thing they told her was that a giant flood was going to submerge North America but, before it did, Martin and a handful of acolytes would be rescued by a flying saucer.

Dorothy Martin wasn’t exactly William Miller but she would do in a pinch. Festinger and his fellow researchers went undercover, posing as believers to gain the trust of Martin and company. What emerged from Festinger’s research was the concept of cognitive dissonance—the stress created when a person holds two contradictory ideas simultaneously. Even when reality clearly failed to line up with belief, Martin continued to believe, as did some (though notably not all) of her followers. One of those followers explained it this way: “I turned my back on the world. I can’t afford to doubt.”

A Perfect Puzzle

May 21 believers couldn’t afford to doubt either. Whenever I met one, I would ask: Is there any chance you might be wrong? Could someone have miscalculated, misunderstood a verse, botched a symbol? Just maybe?

I asked this question of a believer in his mid-twenties. He started listening to Harold Camping’s radio show in college and immediately went out, bought a Bible, and immersed himself in it. After graduation, he took a job as an engineer at a Fortune 500 company; a job he loved and a job he quit because he thought the world was ending. He wrote the following in his resignation letter: “With less than three months to the day of Christ’s return, I desire to spend more time studying the Bible and sounding the trumpet warning of this imminent judgment.”

He would not entertain the possibility, even hypothetically, that the date could be off. “This isn’t a prediction because a prediction has a potential for failure,” he told me.

“Even if it’s 99.9 percent, that extra .1 percent makes it not certain. It’s like the weather. If it’s 60 percent, it may or may not rain. But in this case we’re saying 100 percent it will come. God with a consuming fire is coming to bring judgment and destroy the world.”

I encountered this same certainty again and again. When I asked how they could be so sure, the answers were fuzzy. It wasn’t any one particular verse or chapter but rather the evidence as a whole. Some believers compared it to a puzzle. At first the pieces are spread out on a table, just shards of color, fragments of meaning. Then you assemble, piece by piece, finding a corner here, a connection there, until you begin to make out a portion of the picture, a glimpse of the scene. Finally, you only have a few pieces left and it’s obvious where they go.

A psychologist might call this confirmation bias, that is, the tendency to accept only evidence that confirms what you already believe, to search for pieces that fit your puzzle. We’re all guilty of it at times. But that label doesn’t fully explain the willingness to suspend disbelief: Believers selectively accepted evidence that caused them to quit their jobs, alienate friends and family, and stand on street corners absorbing abuse from passers-by. There is something else going on.

It’s been noted by scholars who study apocalyptic groups that believers tend to have analytical mindsets. They’re often good at math. I met several engineers, along with a mathematics major and two financial planners. These are people adept at identifying patterns in sets of data, and the methods they used to identify patterns in the Bible were frequently impressive, even brilliant. Finding unexpected connections between verses, what believers call comparing scripture with scripture, was a way to become known in the group. The essays they wrote explaining these links could be stunningly intricate.

That intricacy was part of the appeal. The arguments were so complex that they were impossible to summarize and therefore very challenging to refute. As one longtime believer, an accountant, told me: “Based on everything we know, and when you look at the timelines, you look at the evidence—these aren’t the kind of things that just happen. They correlate too strongly for it not to be important.” The puzzle was too perfect. It couldn’t be wrong.

Not that believers didn’t have their doubts in the beginning. Everyone I talked to assured me that they, too, weren’t sure at first. But after a certain point, maybe without consciously realizing it, they made a decision to abandon those doubts, to choose to believe. A young mother tried to help me understand the evidence before throwing up her hands. “It’s about the believers and the unbelievers, you know?” she said.

“They’ve been around forever and as much as we’re positive, there are going to be people who are going to question it because they don’t believe, if you know what I mean? If you believed it you’d be as sure as I am.”

“God’s Not Going to Let Us Down”

Some believers stayed up all night. They watched TV or sat in front of their computers, hitting refresh on their browsers, confident that reports of a massive earthquake originating near New Zealand would soon appear. Other believers went to sleep, assuming that they would awaken in the presence of the almighty.

When the sun rose on May 21, they were taken aback. Maybe it would happen at noon. When noon passed, they settled on 6 p.m. When that came and went, some thought it might happen at midnight. Or perhaps it wouldn’t happen until May 21 was over everywhere on the planet. “It will still be May 21st in American Samoa (last time zone before the International Date Line),” someone posted on Latter Rain, an online forum for believers.

By Sunday morning, new theories were floated. “It was God’s plan to warn people. It was His purpose to hide the true meaning behind May 21. It’s about us suffering what He went through,” a believer commented. One hypothesis had it that three days would elapse before the actual rapture, just like the three days between Jesus’s crucifixion and resurrection. Someone else wondered if it might be seven days considering that seven is a holy number, or forty, the same amount of time Noah was forced to sail around with a boatload of animals.

When those deadlines passed, another narrative took shape. What happened was a test. God knew that believers would be mocked when He failed to return on the assigned date. Would believers hold firm or would they allow the jeers of the world to weaken their resolve? The Lord was separating the wheat from the chaff, they liked to say, paraphrasing Matthew 3:12. It helped that Camping, before he vanished from the airwaves, had seemed to endorse this view.

When a prophecy fails, it’s crucial that a group’s leaders provide an alternate explanation of what happened, or what didn’t happen, according to Lorne Dawson, a professor of sociology at the University of Waterloo, who has studied apocalyptic sects. “The followers of the group are so heavily invested that they have tremendous incentive to accept these rationalizations,” he said. But the revised story needs to be issued rapidly—wait too long and your followers will fall away.

The conversation shifted from why there was no earthquake on May 21 to whether the “door to salvation” was now closed. Rather than believers getting called up, as they expected, perhaps non-believers had been shut out, forced to continue on minus any hope of eternal life. The proofs for this were elaborate and hard to follow, much like the proofs for May 21, and constructing them provided a much-needed outlet for the intellectual energy of the more studious believers.

Now that there was no possibility of salvation, there was no obligation to spread the message. Indeed, there was nothing to do except wait patiently for October 21 when the earth would be divinely incinerated.

As it turns out, believers had insisted for years that the earthquake and the rapture would take place on May 21—but the world wouldn’t be destroyed by fire for another five months. This wasn’t a new date. They knew all along that October 21 was significant. Believers concluded it was God’s merciful nature that had spared the unsaved the terror and torment of an earthquake. “If we have to endure til October 21, I’ll prayerfully do it with a merry heart,” a believer wrote online.

While there were no public displays in the lead up to October 21, there were powerful private emotions. “Of course I’ll be disappointed if it doesn’t happen,” a believer who had helped organize the RV caravans prior to May 21 told me. “But I feel like God’s not going to let us down.”

A father of three boys who works in the financial industry told me he was fairly sure this would be the end. Not a hundred percent, but close. After May 21, his faith was so shaken that he apologized on Facebook to the friends he had tried to convert. But as October 21 drew closer, he found himself wanting to believe again. “I’ve been convinced for 10 years that this would be it,” he said. “I think it will be the end of everything.”

Another engineer I came to know had spent most of his retirement savings, well over a half-million dollars, taking out full-page newspaper ads and buying an RV that he had custom-painted with doomsday warnings. Even when I pressed, he wasn’t willing to admit any doubts about whether October 21 would really, finally, be it. “How can you say that when you see that all this beautiful information is in the Bible?” he asked me, his voice rising. “How can everything we’ve learned be a lie?”

“I Was Part of a Cult”

What happened after May 21 matches up fairly closely with what scholars of apocalyptic groups would expect. The so-called disconfirmation was not enough to undermine the faith of many believers. From what I can tell, those who had less invested in the prophecy were more likely to simply give up and return to normal life. Meanwhile, those who had risked almost everything seemed determined to reframe the prophecy, to search the scriptures, to hang on to the hope that the end might be nigh.

I was struck by how some believers edited the past in order to avoid acknowledging that they had been mistaken. The engineer in his mid-twenties, the one who told me this was a prophecy rather than a prediction, maintained that he had never claimed to be certain about May 21. When I read him the transcript of our previous interview, he seemed genuinely surprised that those words had come out of his mouth. It was as if we were discussing a dream he couldn’t quite remember.

Other believers had no trouble recalling what they now viewed as an enormous embarrassment. Once October came and went without incident, the father of three was finished. “After October 22, I said ‘You know what? I think I was part of a cult,’” he told me. His main concern was how his sons, who were old enough to understand what was going on, would deal with everything: “My wife and I joke that when my kids get older they’re going to say that we’re the crazy parents who believed the world was going to end.”

In the beginning, I was curious how believers would react, as if they were mice in a maze. But as time went on I grew to like and sympathize with many of them. This failed prophecy caused real harm, financially and emotionally. What was a curiosity for the rest of us was, for them, traumatic. And it’s important to remember that mainstream Christians also believe that God’s son will play a return engagement, beam up his bona fide followers, and leave the wretched remainder to suffer unspeakable torment. They’re just not sure when.

Among those I came to know and like was a gifted young musician. Because he was convinced the world was ending, he had abandoned music, quit his job, and essentially put his life on hold for four years. It had cost him friends and created a rift between some members of his family. He couldn’t have been more committed.

In a recent email, he wrote that he had “definitely lost an incredible amount of faith” and hadn’t touched his Bible in months. These days he’s not sure what or whether to believe. “It makes me wonder just how malleable our minds can be. It all seemed so real, like it made so much sense, but it wasn’t right,” he wrote. “It leaves a lot to think about.”