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Mary Karr is a poet, essayist and memoirist. This essay is adapted from her new book, “The Art of Memoir.”

On the first day of a memoir class, I often try to douse my students’ flaming certainty about the unassailability of their memories. So I fake a fight with a colleague while a videographer’s camera whirs in back. Then I ask the class to record what it just saw.

For the caliber of grad students I teach, you might think the exercise would be a slam dunk. Syracuse University’s MFA program receives almost 800 applicants for 12 spots, and we choose a brilliant, idiosyncratic mix: In poetry we once turned down a Harvard grad for a gay ex-Marine. In fiction, a Yale summa cum laude lost a seat to a former Barnum & Bailey clown. You’d guess that these bright, mostly young, fairly sensitive witnesses would nail the exchange down to the color of my rival’s socks.

Instead, their recollections are riddled with errors.

Picture a seminar room with tables in a horseshoe arrangement and some 20 grad students, mostly in black, each propping up a foam cup of lukewarm liquid. I explain the videographer by saying a class transcript may help with a book on memoir I’m writing.

Following a script, I apologize for leaving my phone on but claim I have an administrative problem to work out halfway through our three-hour class. At planned intervals, my co-conspirator calls, putatively to ask — harangue? — me about swapping classrooms. The students hear me be jovial and accommodating, though I hustle him off the phone, saying we can talk at the break.

An hour before he’s due, my colleague steams into the room. A 50-ish poet with a shaved head, he has tightened his mouth into a line and is claiming that this is his seminar room. We need to clear out. Now.

The two of us are playing against type. He’s known as low-key and easygoing, and I as — how to say it? — noisy? Southern? He raises his voice. I suggest we step outside. He steps forward, I step back. He’s tall, I’m short. I try to defuse the situation. He says for once I should do what everybody else does and cooperate. He tells me to “go f---” myself — or do I only remember it that way? Then he heaves a sheaf of papers into the air and stalks out. The students are agog. On the video, they cut their eyes away from us to connect with each other.

Paralyzed silence. Am I okay, the needy kid asks, Bambi-eyed.

I explain the ruse, and the group’s burst of laughter reveals a collective awkwardness. One joker claims he’s suing for trauma, since he flashed back to his parents fighting. But when I ask the students to jot down what they saw and share their recollections, the mistakes pop up like dandelions.

It’s not just them. Studies have shown that even the best minds warp and blur what they see. For all of memory’s power to yank us back into an overwhelming past, it can also fail big time — both short term (the lost vehicle in a parking lot, the name at the tip of your tongue) and long term (we made out in high school?).

For example, memoirist Carolyn See recalled her husband bailing on her while she metaphorically held on to his leg. But her children and ex corrected her, saying she’d sent him packing. My late friend David Carr of the New York Times tried to track down the facts about his most deranged coke-fiend years in “The Night of the Gun,” using his investigative skills and a video camera to interview old running partners in Minneapolis. The highlight concerns a face-off with a gun-toting maniac. The big reversal? It turned out David was the maniac wagging the gun. When he recounted that discovery to me years later, the discrepancy still set him back.

In fairness to David’s memory, he was strung out at the time, but still. How can the mind get things so right, yet so wrong? Neurologist Jonathan Mink explained to me that with memories as intense as David’s, we often record the emotion alone, all detail blurred into an unreadable smear.

That’s dangerous. False memories can end careers and ruin lives. Just ask Brian Williams, who was forced to give up the “NBC Nightly News” anchor chair after he embellished a story about a helicopter mission during the Iraq War. Or presidential candidate Ben Carson, who’s under fire for two tall tales he told: one about being offered a scholarship to West Point and another about trying to stab a friend in childhood. Or James Frey, who was taken to task — by Oprah, no less — when his “memoir” “A Million Little Pieces” was found to contain significant exaggerations.

I make this point to my students after the staged fight, and we review the blunders. I correct details on the board, fix dialogue and interpretative errors. By the end, we’ve chalked up an agreed-on version. During this time, I sometimes implant new “facts” — I give my adversary a leather bracelet he doesn’t wear and even have him fiddle with it nervously.

A month after the event, when asking the students to render the fight on a page, I’ll mostly get fed this official account. What the group deems right almost always obliterates anybody’s original recollections. It’s the power of groupthink, the basis of both family dynamics and most propaganda.

But worse than the groupthink that warps memory are the students’ original, radical misjudgments. Poets and trained musicians seem mysteriously keen at nailing dialogue verbatim. But they can still flub tone or even misattribute who said what. I was the one saying, “We can work this out.” But some credit my opponent with the phrase as I jerked my elbow away. Some heard me exasperatedly sighing, “We can’t work this out.”

Who knows why half the class recalls my advancing toward my colleague, when I either stood still or backed up? Even my inertia, if they observed it at all, is recorded in almost military terms: Sentences such as “She held her ground” or “She was sturdy as a bulldog in her stance” appear, and I am likened to granite or steel. One year a saxophonist and hip-hop DJ was so convinced by our acting that he almost left his seat to stop the brute assaulting me. Yet even in possession of the facts, this young man wound up speculating as to “what Mary had done to make him attack her like this.”

The students’ innate prejudices shape how they view things. One year when I claimed that the phone calls were from a doctor’s office, a student with a serious illness worried about me, while everybody else just resented my answering during class. One guy figured that my colleague and I had been sleeping together, and he half-manufactured an insidious narrative of betrayal based on our body language. A young woman who’d had a stalker figured that he was one. Somebody else thought we were both high.

I come from a family of storytellers, and it’s true that having a close group of folks retell events over and over better logs the narratives into long-term storage. But memorized language can also calcify what’s in your head. Events grow stale when told by rote. Painful events recounted for humor can be drained of the real pathos or terror they first registered.

And negotiated memories can be like a piece of writing clawed over by an overzealous editor — anything dubious is deleted and any particular point of view abolished. Anybody in a family knows how tyrannical groupthink can be.

Not long after my first memoir came out, my mother and sister started ringing up and using my own language to recount scenes I’d written about. As a younger sibling whose views tend to be heavily discounted, I might have registered this as a triumph — finally they get it! Instead, I felt bereft. I had inadvertently become the official chronicler of our collective memories, and who knows what I was screwing up? Part of me longs for the old days, when I couldn’t open my mouth without hearing about how something happened only a few times or wasn’t that bad. In a warped way, that was way better: It kept me folded more safely in the family delusion system.

Twitter: @Marykarrlit

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