David Nott is trying to explain why, after more than 30 years, he still feels the compulsion - he's previously called it an ‘addiction’ - to travel to the world’s most dangerous places, rather than see out his medical career in the relative comfort of his London hospital.
“If you watch something on the television and it's so terrible, there's this burning," he said.
"The flame starts going off in my heart, and it starts getting stronger and stronger and stronger until I really have to go.
"There's nothing I can do about it. It's a very strong impulse to go and help people.
It is an impulse that has seen the man known as the “War Doctor”, or the “Indiana Jones of surgery”, journey around the world’s trouble spots - from Afghanistan to Iraq to Syria - using his skills to help the innocent victims of war and disaster.
Seven years ago, he set up an organisation with his wife, Elly, with the aim of passing on his skills to other surgeons.
The David Nott Foundation has so far helped more than 800 doctors around the world.
Recently, with the help of famous neurosurgeon Henry Marsh, he has put together a 12 hour symposium on surgical techniques which every doctor in Ukraine can access on their smartphone.
"When the Ukraine crisis started, I knew that this was going to be something that the Ukrainian doctors had never seen before,” Doctor Nott told Adrian Masters in this evening’s (Thursday 7 April) Face to Face programme.
He said: “They've never seen war, they'd never seen what it’s really like to have to deal with bomb blast injuries, gunshot wounds, fragmentation injuries, things like this.
"And they also need to be able to sometimes work in environments where they don't have many resources. Like blood [for transfusions], or their CT scanners don't work anymore, or the electricity goes down and the generators don't work.
"So we need to take them back a step to what they were trained for right at the very beginning. To use a stethoscope to be able to understand what to do with the patient and to make very difficult decisions.”
They are skills David wishes he had had when he started out 30 years ago.
He had recently qualified as a surgeon when he joined the organisation ‘Medécins sans Frontières.’ His first assignment was to war-torn Sarajevo, at the height of the Bosnian conflict.
An incident during the trip taught him about the challenges of carrying out surgery in a war zone.
“Our operating theatre was underground because the hospital had been targeted all the time," he said.
"It was called the State Hospital but it had so many holes in it it was called the “Swiss Cheese” hospital by lots of people.”
All the other surgeons had fled, so he had the operating theatre to himself.
He recalled: “At about midnight, a load of bombs went off and a boy was brought in with shrapnel in his tummy. And so we decided to take him to the operating theatre and he was bleeding.
“But during the operation, suddenly there was this enormous crash and the hospital just shook, my feet shook and the lights went out and it was completely dark.
“I was left with the boy on the operating table with a big piece of shrapnel in his abdomen. I’d seen that the fragment was in a very precarious position and that I needed to remove it, but very carefully. If I’d just taken it out he would probably have bled to death.
“I stood there for a while calling out to people, and nobody answered my call. And then all of a sudden, about 15 minutes later, I could feel this boy going and going, and I could feel the pulse getting less and less, and I knew that this was not going to end well for him.”
Finally the hospital generator came back to life and the lights started glowing dimly.
But the boy had died and David found he was alone in the theatre.
“Everybody else had just run for their lives," he said.
"In war that's what happens. But it’s a very difficult decision to make. If you have a patient with you, what do you do? Do you leave the patient ? Do you run?
"I think the reason why I go out and help people is because I'm passionate about helping in very difficult environments. I do put patients before myself. And I think that if the situation ever arose again, I would stay there again.”
The Carmarthenshire-born surgeon says he found his vocation just after finishing at medical school.
He was taken by his father - an orthopaedic surgeon - to watch the film ‘The Killing Fields’, about journalists uncovering atrocities committed in 1970s Cambodia.
But he told Adrian that his desire to help others was cultivated much earlier; while living as a child with his grandparents in the west Wales village of Trelech.
He stayed with them while his mother completed a nursing qualification and his father worked in the north of England.
He said: “The family I had at that time instilled into me a way of looking after everybody else. I think the older you get, the more you relate to your childhood, and the more you think about why you do things the way you do.
“And I think that it's a matter of something subliminal that was put in my head by ‘Mamgu and Tadgu’, all those years ago.
“That instilled the desire to go and help other people."
Now in his mid-sixties, David has not ruled out coming back to Wales to live with his wife and two young daughters.
And when he dies, he knows exactly where he wants his ashes to be scattered: in Trelech, from “the little bridge overlooking the little river.”
“I think I feel more Welsh now than I used to before," David explained.
"I enjoy speaking Welsh to those I can speak it to. I have an enormously strong connection now with Wales.”
Watch David Nott’s full interview with Adrian Masters on Face to Face on ITV Cymru Wales at 10:45pm on Thursday 7 April