He has been walking around the world for the last 27 years—Here’s the no. 1 lesson he learned about happiness

Karl Bushby was 29 when he left his home city of Hull, England and took off for the adventure of a lifetime. With $500 in his pocket and some survival gear, he went on a mission that no one else in history had ever completed: walking an unbroken path around the world.

Bushby's journey, called the "Goliath Expedition," began in 1998 in Punta Arenas, Chile, a city near the southern tip of South America. It's brought him across continents including the Americas, Asia and Europe, and ultimately ends with the goal of arriving back in the United Kingdom.

"The objective was simply to get home unassisted by any form of transport," Bushby told CNBC Make It.

Throughout the journey, Bushby has followed two rules: He can only walk or swim, unassisted by any form of transportation, and he cannot return home to Hull, England, until he arrives entirely on foot.

"These sounded like two simple rules from the early days, but you know, once those two rules meet the reality of the real world, things can get mighty complicated, especially [with] visas and difficult governments and regimes and some of the controversial borders that [I've] had to cross," he said.

After walking about 30 kilometers a day, along with some unexpected setbacks, Bushby has now made his way into Europe and expects to complete his journey and return home to England next year, he told CNBC Make It.

Bushby has always been an adventurer. He says he used to go explore all day with his brother before returning home for dinner.

Growing up in a military family, he was inspired by his father who served in the British army. Bushby also joined the army at age 16 and served as a parachute regiment for about 12 years before taking off on his expedition.

At a certain point during his tenure in the British army, Bushby got bored.

"I spent my 12 years in the British army waiting to go somewhere we never really went, other than Northern Ireland," he said. "We happened to be living through one of the most peaceful times in history," he said.

"So we got bored and tired and became wondrous and mischievous," he said. "At some point, I started drawing lines on maps and daydreaming about great distances and distant horizons, and one thing led to another."

One day, Bushby drew a line from the United Kingdom over Europe and Asia, through Siberia, over the Bering Strait, into North America and through to the bottom of South America.

"Once I got that on a map, there was kind of no going back ... The old hairs on the back of your neck stand up," he said.

So, in 1998, Bushby left the British army to begin the long journey. He took a military flight from the United Kingdom to the Falkland Islands, then a civilian flight to Punta Arenas, Chile, which was the starting point of his expedition.

"That first day you step onto the road [is] a memorable one, because at that point, you're a long way from home. You've burned all the bridges. You told everyone you'd rather die than come home," said Bushby.

"You got like 500 U.S. dollars in your pocket, no support, no idea how it is going to work out, just absolute faith that you can somehow make it work. And you're on a road that is about 36,000 miles long, with very little idea of what's coming. I mean ... you're further than a man mission to Jupiter at that point," he said.

Bushby's journey over the last 27 years has brought him through many close encounters.

He has famously crossed the Darien Gap, been detained by Russian authorities, jailed in Panama, nearly frozen to death in Alaska and swam across the Caspian Sea over a 31-day-period.

On top of all of this, he's gone days without food after walking for many miles, relied on strangers for medical help and ended many nights by himself in a tent he pitched on the side of the road.

"The psychology of hunger is interesting. It's not something that most of us are really used to. When you have no idea where your next meal will come in, you just become obsessed with finding things to eat," said Bushby.

"You'll see food everywhere, every shadow, every rock, looks like something you can eat. You'll end up running around, chasing hallucinations most of the time," he said.

Despite all of the challenges he's overcome, one of the biggest lessons he discovered throughout his journey didn't have much to do with physical pain or endurance. Rather, it was about happiness and how it ultimately comes from your relationships.

"If you would ask me, what was the hardest thing you've done over the last 27 years – that is losing the women that you fall in love with hands down. That's the toughest thing you will deal with… The physical stuff – pain is easy, suffering is different," said Bushby.

On the other hand, he said: "The happiest of times was when I [was in] those relationships. When you're with somebody."

He's also learned that people are generally very kind, across all cultures and regions in the world. Many times throughout his journey, he says he's been taken in, fed and cared for by strangers who ask for nothing in return.

"You don't even speak the same language, so it's just about smiles and nods and then they send you on your way ... It's just one story after another, and it's across every culture, across every country," he said.

"This world is hell of a lot friendlier and nicer than it might appear."

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