In the summer of 1991, I landed an internship with a major business magazine. I cobbled together a "young professional" wardrobe, moved into a New York University dorm, and took the subway to midtown Manhattan every weekday.

There, in a gleaming high-rise, I spent about 10 weeks learning the skill of fact-checking. Every word that got published in the magazine had to pass through a rigorous process in which young reporters checked and double-checked the truth and accuracy of every story, headline, chart, and photo caption.

Most fact-checkers are aspiring writers, and checking someone else's work provides good training. It teaches you the right questions to ask, and it teaches you to pay attention to the details. It also establishes accountability long before the story goes to press, as writers know they'll be turning over their notebooks and having their work dissected for accuracy.

It's not a glamorous process. In truth, it can be so tedious that Jay McInerney uses fact-checking to illustrate the desperation of his protagonist in Bright Lights, Big City. You may, for example, have to call a man being accused of extortion and ask him questions like, "Is it true that you ran track in high school? Is the wallpaper in your office burgundy?" If it's in the story, it must be proven.

The Internet existed in 1991, but just barely, and we interns certainly didn't have it in our small, windowless office. Every Monday, an editor would deliver us a manuscript of an upcoming story. We'd meet with the writer, who would turn over interview tapes, phone numbers, newspaper clips, annual reports, and other supporting documents. Then we'd start working through the stories, underlining every verifiable fact, then putting a check mark underneath when we'd proven it. We had to leave room for a second set of check marks, because back then, at least at this particular magazine, everything got checked twice.

Not every publication still checks its facts, but Rolling Stone does. That's why so many readers, especially those of us who have ever worked as fact-checkers, just can't quite understand what went wrong when it published a piece detailing rape and sexual politics at the University of Virginia.

There are big, theoretical debates about the story written by Sabrina Rubin Erdely - how much of it is true, and what behind-the-scenes negotiations took place to get it to press.

But we fact-checkers, past and present, are pondering the minutest of details. That's what we do.

I checked facts for several other publications. I doubt I ever checked a story that was perfect, and I doubt I ever wrote a perfect story of my own. Most errors are so small they can feel inconsequential. Maybe that company earned $2.78 billion last year, not $2.76 billion. But a mistake is a mistake. If you get the little things wrong, people are less likely to believe that you got the big things right.

And it's different when reputations are on the line.

In Erdely's story, if the man who allegedly led "Jackie" into a gang rape wasn't a lifeguard, it doesn't mean he didn't attack her.

If "Jackie" named the wrong fraternity house, it doesn't mean she didn't get raped.

But the second we learn the accused man wasn't a lifeguard, and Phi Kappa Psi didn't have a party the night Jackie said they did, we can't help but wonder what else is wrong with the story. Some people will see that as a failure on the woman's part, and some will blame Rolling Stone.

There's no happy outcome here. If every detail is true, then a woman was brutally gang-raped. If every detail is false, men's reputations have been unjustifiably ruined.

If the story is true, but includes errors, that's still not much to hope for. An error-laden story about vicious crime takes a toll on the credibility of accusers and seriously damages the reputation of the publication. The editor has shifted some blame from Jackie to himself, but in the days of 24-hour cable shows and unfettered comments sections, we already know that the incorrect facts have been enough to discredit Jackie in many readers' eyes.

When the little details are wrong, it doesn't mean that the big ones are, too. But it means that the reader can't believe you anymore. Not every fact can be confirmed with a simple check mark, but Rolling Stone and the story of Jackie provide a stark reminder that what can be proven must be proven.