That's how a crime scene investigator (CSI) copes. At any crime scene, he or she is surrounded by evidence of mankind's capacity for evil.
So police brass tapped five of these men to help New York authorities climb through the smoldering remains of two of the world's tallest skyscrapers to determine exactly what happened and to help recover bodies.
Even such men, however, with their steely psyches and practiced detachment, were unprepared for that week's work.
With the 10th anniversary carrying its own force of inevitability, the CSIs have little choice but to remember.
Mike, John, Leo, Mark, and Terry. Vincent, Taggart, Rahill, Fisher, and Lewis, if you prefer surnames. Four cops, one civilian.
For them, this is a tricky week.
Michael Vincent: "I'm kind of a black-and-white person," announced the 59-year-old officer of 30 years and counting. "You're going to have to pull the information out of me."
John Taggart: "Believe me, a year or two in here is like 10 years anywhere else - just the amount. It's a very violent city." The officer, 49, of Roxborough, seldom gets emotional. What he means is that CSI work is different from most other police assignments. He used to take photos of mummies at the University of Pennsylvania Museum of Archaeology and Anthropology before joining the force 20 years ago.
Leo Rahill: "A normal person is not designed to see death on a daily basis," said the 54-year-old civilian member of the crime lab. Rahill is a former housepainter from South Philadelphia who joined the force in the mid-1990s. Chattier than his colleagues, he said of CSIs: "Everybody has this stupid way of turning off that piece of your brain that wants to run down the street screaming."
Mark Fisher: "Seeing things in New York was life-changing," said the 30-year police veteran who was a crime lab lieutenant at the time. Fisher, 52, of Northeast Philadelphia, is married to his high school sweetheart. "Thank God for my wife."
Terry Lewis: "I remember like it was just today," said the 40-year-old officer. On the force since he was 19, he lives in Northwood. He cries at movies but not at crime scenes because he has the "off" button needed to survive in his job.
Vincent was the first of the five at ground zero.
He and several superiors arrived on Sept. 12. They reported back to headquarters that the situation was awful, the need for help extreme.
"It was above overwhelming," Vincent said. "It was something you couldn't imagine."
John Timoney, Philadelphia police commissioner at the time, dispatched four more CSIs.
The next day, Taggart, Rahill, Fisher, and Lewis were contacted. Each said yes. No hesitation. Taggart didn't even have time to pack underwear.
The four piled into the unit's Ford Expedition with the essentials: "A few changes of clothes, camera, film," Rahill said.
"Body bags," he added.
It was evening as they approached New York, the twin towers erased from the skyline. More chilling was ground zero, where 2,753 people perished.
"You see a three-square-city-block area of friggin' rubble that is 10 to 15 stories high with fire hoses spraying down on it, and you're saying, 'My God, there's got to be 5,000 people in there,' " Rahill said.
They connected with their CSI counterparts in the New York Police Department, a crew coated in dirt and fresh with stories of the day's perils. They had suspended their search three times that day, they said, because a horn had sounded to warn that an adjacent building might collapse.
"Pick a way to run and hope you pick the right way." That's what the New York CSIs had done. That's what you'll have to do, too, Taggart recalled being told.
The New York team explained the next day's task: There were limbs on the roof of the Millennium Hilton near the rubble of the towers. They'd need to be recovered in the morning.
"Cool," Taggart said. "Let's go."
The men drove to a hotel they'd been assigned, the Paramount, in the theater district. They were surprised at how lavish it was. They'd expected to be sleeping on cots or a church floor.
"It was right next to The Lion King," Taggart recalled. Times Square was still. No cars. It was baffling.
The next morning, at the Millennium, their job was to gather human remains and airplane parts.
"There was just" - Taggart hesitated - "we filled up three body bags full of arms and legs."
It took 40 minutes.
"That was a little weird," he said, coughing up a faint nervous laugh. "It's not something you see every day."
At the base of the building was a portion of jetliner fuselage, some of its seats still intact. Without emotion, he analyzed everything he saw.
"It didn't make sense that these body parts are on this little small roof when you have all these other buildings around it. How did they get there? Hard to explain."
Lewis was mystified as well. "It was just eerie walking through that office space, and you could just tell people had dropped everything and gotten out of there," he said.
Thinking back a week ago on the search, Taggart wondered how he'd been able to hold his emotions in check. "I never saw a face, never saw a head, never saw a full body," he said.
An ex-smoker, he chomped through Life Savers, one after another. Then a jarring memory spilled out.
"We went to the morgue that one day. We took those parts, we drove those parts in the front of a front-end loader, to the morgue.
"I remember doing that now," he said, his voice slowing. "I remember doing it."
Fisher found a memory of an empty office haunting him this week.
"In the middle of a building was a foot with a shoe on," he said. "I remember thinking, how on earth did this get here, and where's the rest of this person?"
But what really got to these men were the hundreds of anxious loved ones standing near the recovery scene with photos and fliers, begging investigators for information. Fisher collected their offerings, though deep down he knew he could do little to help.
"Dealing with the dead is different. But dealing with the living, when you look in their eyes and they really want to find their loved ones, that's really difficult."
One day in the rubble, Fisher came upon a fireman's uniform. To his left was a searcher, the dead fireman's brother. The searcher watched as firefighters removed the body, covered it with an American flag, and carried it away on a stretcher.
"Just looking at the tears in his eyes as he was holding onto his brother's coat was really -" Fisher began crying himself.
Vincent was stoic in his own recollections. After meeting up with his Philly unit, he went about the same grim work. He came across human remains only three times.
Lewis remembers coming upon a leg from the knee down, shoeless, with nail polish on the toes.
"We had a job to do," Fisher said, "and we wanted to do it with respect and dignity."
Driving back to their hotel after one 12-hour day, the CSI team was stunned to pass what seemed like miles of supporters standing along a Manhattan freeway. The people were cheering, clapping, and waving American flags for the first responders.
Rahill cried at the sight of it. Taggart scolded him. Rahill pulled himself together.
"I'm glad that happened," Rahill said of his tears. "Made me realize I was still human, you know?"
They returned to Philadelphia on Sept. 20. The next year Vincent retired and moved to Orlando, where he works for the Orange County Sheriff's Office. His daughter is an officer at the crime lab he left behind.
As a high-ranking CSI in Florida, Vincent spent three years working the Casey Anthony homicide case, which ended this summer with an acquittal. He was so disappointed in the verdict he didn't answer his phone for two days.
Another subject he avoids is the time during a narcotics raid when he took a bullet to the shoulder and his gun arm went limp ("It's an emotional thing" is all he'll say).
In another category altogether is his time at ground zero.
"I didn't talk about it," Vincent said, "because I didn't want it to affect me the way it affected some people."
Fisher today is a captain and commander of the department's firearms training unit. His two sons are police officers, his daughter is a nurse, and his wife, Sue, is his rock. On the 9/11 anniversary this weekend, he plans to put all his energy into helping run the department's annual Family Day.
"I refuse to give in to terrorism," he said, "and dwelling on terrorism."
Since 9/11, Lewis has gone through an amicable divorce. He has assumed administrative duties at the crime lab, and helps on cases only when staffing is tight.
He tries to appreciate every day. "You never know when it's going to be your time to leave this Earth," he said.
Last week, at home with his second wife, Jeannette, Rahill pulled out 800 photos from ground zero that he and his coworkers had shot and developed. He hadn't looked at them in nearly a decade. With retirement on his mind, maybe he will pass them on to his three sons from his first marriage.
"This is my legacy - something I did in my life," he said, pointing to the pictures.
What would he tell his children?
"Your old man did something in his life that meant something." He fought back tears.
Kathy and John Taggart have known each other since they were teenagers in West Philadelphia. She is convinced her husband came back from ground zero a different man.
"I don't really know the depth of what he saw," she said. "He's just different. He's not as open. He's so serious."
At the time of the attacks, Taggart's father was ill. He and Taggart's beloved aunt died a few years later.
Taggart's father had not talked much about the 26 bombing missions he'd made as a tail gunner on a B-17 in World War II. His son can only speculate as to why.
"Being shot at at 30,000 feet in a goddamn tin can."
The day after Taggart returned from ground zero, he walked into his father's Delaware County home.
"How was it?" the elder Taggart asked.
"It was pretty wild, Dad," he replied.
That was that. Two veterans of a war zone.
"But I mean" - Taggart's eyes began to well up and he had trouble speaking - "we both knew that we dug each other."
Taggart has ordered 400 small American flags. On Saturday, he will plant them all in his small lawn, for the roughly 400 firefighters, police, and Port Authority officers who died in the 9/11 attacks.
With that, he will say all there is left to say.
See videos from stories of people whose lives were affected by Sept. 11, 2011, and find more 10th anniversary coverage at www.philly.com/9-11
Contact staff writer Maria Panaritis at 215-854-2431, firstname.lastname@example.org, or @panaritism on Twitter.