He has scaled four mountains higher than 8,000 metres (26,250 feet), and most recently completed Pole2Pole, a two-year circumnavigation of the globe unassisted and with no motorised transport. He’s also appeared on French television, taking celebrities on survival trips in the wilderness – just like Bear Grylls.

Horn was in Hong Kong recently for a stopover between missions, and to inspire schoolchildren with an important life lesson he has learned – the difference between motivation and discipline.

“You don’t think you can become an explorer. I think you are born to be one,” Horn explains, sipping coffee on his gently rocking boat.

The 53-year-old is fit and trim, and enjoys a lifestyle that’s the polar opposite to that of workers chained to their desks. The father of two daughters, Annika, 25, and Jessica 24, likes to embark on his adventures alone, a trait that began in his childhood.

Born in the mid-1960s in Johannesburg and raised in Stellenbosch, Horn was an adventurous and athletic boy who played a variety of sports including rugby and cricket.

“I had a free mind, and it happened to be outside rather than inside,” he explains. “When I had my first bicycle, my parents just gave me one rule: to be back home by 6pm, and I didn’t have to tell them where I was going. With a bicycle I could go anywhere. I would come home at 6pm and I would describe everything I did.”

Marine explorer Jacques Cousteau was a childhood inspiration, and the only television show he was allowed to watch was The Undersea World of Jacques Cousteau. When he was about 12 years old, Horn’s father encouraged him to write letters to the French explorer, asking if he could work for him, but never got a response.

Horn says his parents, both university lecturers, were very liberal with his upbringing, for which he is grateful.

“A lot of what I do today was due to how I was brought up and educated. I never strayed from those ideas, but also focused on what I was taught. With the freedom that my parents gave me, my dreams just grew bigger and bigger.”

Later, Horn learned survival skills during three years in the special forces unit of the South African Army. As a 17-year-old he was chosen from a pool of 4,000 young men that was whittled down to 400 and then 40.

When he was sent to Namibia and then Angola, Horn fought communist insurgents in close combat, set up landmines and other explosives, conducted tracking and gathered intelligence behind enemy lines.

It was in the army that Horn came to appreciate discipline, and insists it is more important than motivation.

“People think we should be motivated every day, but that’s a load of crap,” he says. “Who is motivated to jump into a river where you might be eaten by crocodiles, piranhas, parasites, things like that? What you need in life more than motivation is discipline – the discipline the military and my parents taught me.

“Discipline gets you out of the tent earlier than others would … That motivation is profound and sincere. It takes discipline to get out of the tent at minus 60 [degrees Celsius; minus 76 Fahrenheit] when that may be the last time you get out of the tent. How can you be motivated to do that?”

At 24, Horn gave away all his possessions and went to Switzerland, where he hitchhiked to a small town in the Alps, learned how to ski and later tried canoeing, kayaking and canyoning.

Horn was once asked to jump down a waterfall for a watch advert. He says it was the ballsiest thing he ever did.

“I was young and I was wild; I wanted to start a career in the world of sport and live professionally from it. I needed to do what I thought was big and make people dream,” he says.

From then on, Horn realised his dream of being an explorer was within his grasp. His first expedition, in 1997, was to the Amazon, where he hung on to a fibreglass board and swam down the river with fins. But he wasn’t completely reckless.

“The advantage I had coming from the military was I could join other special force units on exchange programmes. I joined the Brazilian special forces, and they trained the American forces for the war in Vietnam,” he explains, and they gave him a course in jungle survival training.

“The Amazon always fascinated me as a child, as the polar regions and mountains did. I thought that to get enough knowledge, I should first swim 7,000 kilometres down the Amazon with this board and hunt to survive to see if I could make it,” he says.

He started from the Pacific Ocean, walked to the source of the Amazon, and swam the entire length of the river to the Atlantic Ocean.

When he’s not planning or out on expeditions, Horn has parlayed his knowledge and experience to motivational speaking. He helped coach the Indian cricket team that won the World Cup in 2011 and the German soccer team that won the 2014 Fifa World Cup. Again, he reiterates that it’s not motivation but discipline that’s needed.

“I told them, ‘You guys are playing a game. We all compete to win, but if you lose once or twice it’s OK for you. But I cannot lose. The moment I go to the North Pole – when I lose, I lose my life’,” he says.

“The moment I make that decision to go, I’m fully committed, whereas a sportsperson can still run on the field, or skip a training session. They are half-committed.”

Once everyone is fully committed, says Horn, the team players are more focused, and can play with more freedom, with motivation and discipline. He says honesty is also important.

“Just knowing exactly what you can do and not bulls***ting about it creates honesty. In a team environment, you’ve got to know what your team players can do. If you expect more from them and they can’t deliver, it’s going to put pressure on them and you get disappointed, and that creates this downpour of negative thought,” he says.

Horn is now preparing for his next expedition. In August or September, he will sail in the Arctic Ocean until the Pangaea hits ice, and then walk across the North Pole via Greenland or Spitsbergen, an island in a Norwegian archipelago north of Iceland.

In the meantime, he’s going to Alaska for training and will then attempt to climb K2, the world’s second highest mountain, from the Chinese side.

His wife, Cathy, who he met in Switzerland, was the backbone of Horn’s career, helping him with all the planning and logistics of his expeditions. Her death in 2015 hit Horn hard, and he thought he should be home with his daughters. However, they persuaded him to go back to doing what he loves, and took over his late wife’s role.

As he gets older, Horn admits it’s getting harder physically to complete his expeditions, though with experience he’s more energy-efficient.

“I often say that before, when I had to hit a nail into wood, I used my strength in the hammer to hit the nail. Now, I’m using the weight of the hammer to pound in the nail. That’s experience,” he says.

“There is a limit, especially in the world of extreme sports, to age, awareness, balance and recovery. All these things takes a bit longer, but I don’t think I could have crossed Antarctica any earlier than I did because I needed that 25 years of experience. I needed to build a boat. I needed to have the stars aligned to even attempt it.

“When I slow down to a stage where I can’t go out and explore any more, life will tell me. I will go on as long as I can until life tells me that maybe it’s a good idea to stop.”