This is where they admit de feet.

The New York City Marathon devolves into a Greek tragedy for ill-prepared runners at an unsuspecting half-mile stretch of the Upper East Side — where quitters are statistically inclined to rip off their racing bibs, The Post has learned.

The highest number of runners tap out every year at Mile 18 — a dreaded marker the race organizers have dauntingly dubbed “The Wall.”

Last year, 203 runners vanished between mile 18 and 30K, marking the highest loss of runners between two timing points, according to Road Runners data.

That 0.64-mile stretch lies along a fairly quiet stretch of First Avenue from 96th to 103rd Street, which is littered with parking lots, sports fields and municipal buildings rather than apartments.

It’s where the wall-to-wall crowds begin to thin out and runners face comparative silence — especially coming off the heels of the deafening roars that greeted them off the Queensboro Bridge just two miles prior.

It also precedes the steepest ramp of the course just before Mile 20 — the Willis Avenue Bridge — for the race’s brief foray into The Bronx.

Some consider that marker to be “The Wall,” while others say the real one is a multi-mile stretch that starts at Mile 18.

Mile 18 has proven to be the most common give-up point throughout the sprawling, five-borough course across the most recent decades, even though it’s nearly 70% of the way into the entire race.

“It’s likely that runners who are having tough days decide to cut their marathon short and wait until they’re back in a convenient location in Manhattan to drop out,” Road Runners told The Post.

Annie Reeves, who ran her first marathon in 2023, says the crowds thin out near Mile 18 — and the race turns into a “mental game.”

“You go through Brooklyn — which is an insane adrenaline rush and amazing experience — you go through Queens, which is great, then when you come off of the 59th Street Bridge, it’s like nothing you’ve ever experienced before,” explained Reeves, of Bayside.

“You go to all of these phases of amazing, unmatched energy where people are pulling you through. And Mile 18 is a low point.”

But Omar Medjid, founder of the World’s Fair Run Crew, theorizes that the pain of Mile 18 is universal regardless of the course.

“That’s when you start looking at your watch, you’re kind of panicking and you’re just saying, ‘Okay, am I going to hit my goal time? Is my pace dropping?’ You start to feel it in your body versus the actual data,” said Medjid, 33, of College Point, who ran the NYC Marathon in 2024.

“You’re already tired from hitting the bridge and everything, then you know you still got that long stretch of Fifth Avenue to go. A lot of mental was really what it would be, but I do think it’s mainly based on the actual mile rather than exactly where it is.”

What pulled Medjid through was seeing his friends and fellow running community members along the route — which helped him remember why he was running the race.

“Remember your why” is a major piece of advice Road Runners coach Steve Mura offers racers when pushing through “The Wall” and toward the finish line.

“Before the race, write it on your hand. Why did you sign up? When those moments get hard, and it will get hard, look down at your hand,” said Mura, the organizer’s director for Runner Training and Education.

“Think about the next mile, not the remaining eight.”

Pack plenty of fuel, keep your eyes peeled for water stations and use the cheering crowds to your advantage, he continued.