Image copyright Hermione Image caption Shachar Bialick aims for Curve to become a $50bn to $60bn business

The BBC's weekly The Boss series profiles different business leaders from around the world. This week we speak to Shachar Bialick, founder of fintech company Curve.

As Shachar Bialick route marched through the surf, his body was aching so much he didn't think he could continue.

The then 18-year-old was doing his initial training for the Israeli special forces. He and the other new recruits had to march for 40km (24 miles), while carrying 40kg on their backs. If that wasn't bad enough, they were making their way along the coast, and had to walk through the sea up to a depth of at least 40cm.

"You can imagine how difficult it was," says the 38-year-old looking back. "After the first 10km I thought there is no way I can continue. Then after you finish the 40km you feel dead, but then you think 'OK I can do that'. It gives you the mindset that everything is possible."

The life of an Israeli special forces soldier may seem a million miles away from the world of business, but Shachar says that the three years he served gave him the determination to succeed in his subsequent career as a serial entrepreneur. "It gave me grit and perseverance, which are clear factors for success in business."

Image copyright Shachar Bialick Image caption Shacha (pictured on the left) spent three years in the special forces

Today Shachar is the founder and boss of a London-based fintech company called Curve. This gives users a bank card and app that consolidates all their banking cards and accounts in one place. So instead of having to carry round a wallet full of different cards, you can just use your Curve one.

It sounds like an idea that would appeal to many people, and Shachar has grand plans for the business he launched back in 2016. "In 10 years time we are going to be IPOed [floated on a stock exchange]... and hopefully worth around $50bn (£40bn) to $60bn," he says.

This is obviously a very bold aim, but Curve's early investors are showing their confidence in Shachar. Back in July, the company secured $55m of new funding that values it at $250m.

Born in Tel Aviv, Israel's second-largest city, Shachar was brought up in the settlement city of Ariel, in the occupied West Bank.

Disruptive at school, but gifted with computers, at 16 he was pulled from his class and sent to study computer science at a university in Tel Aviv. Two years later he had to do his compulsory military service.

After leaving the army Shachar successfully founded and then sold a string of companies, including a door and windows business, and a recruitment firm. He also made time to get the top master of business administration qualification.

Image copyright Curve Image caption Curve allows users to just need one bank card

Despite having money in the bank from his earlier business career, before he launched Curve when he was 36, Shachar says that both his father-in-law and his wife were wondering if he was going to settle on one company.

"I had an intervention [from my father-in-law]," he says. "He said 'what are you going to do with our life?... You can't waste your talent... You won't work for anyone else... alright, go for it."

Meanwhile, his wife was concerned that it could impact on their relationship, as she knew he would dedicate all his time to it. Thankfully, Shachar says that his wife, and both her parents and his, remain "very supportive".

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While he could have based the business in Israel, he says he chose London for a number of reasons, including its long-standing positions as a global capital of finance, and the access to a large number of talented employees.

Curve now has more than 500,000 users across 31 European countries, and over 150 employees. Expansion into the US is due to follow next year. It makes its money from the banking charges retailers pay, the monthly subscription fee for its premium card, and selling other banking services.

Image copyright Curve Image caption Shachar chose London for Curve's head office, rather than a city in Israel

Fintech author and commentator Chris Skinner says that Curve is proving to be increasingly popular.

"Like many UK fintech start-ups, Curve came up with an idea that is unique," he says. "Consolidating all of your credit and debit cards onto a single app and single card has proven to be a compelling proposition.

"Curve's vision, along with many other UK fintech start-up firms, is the reason why Britain has more early stage financial technology firms valued in the millions and billions of dollars than any other place in the world, including Silicon Valley."

As Curve continues to grow, Shachar says he remains thankful for his military service all those years ago.

"When I was 18 I was very naive about life, very lackadaisical," he says. "And they [the Israeli Defence Forces] break you. They change your character, and how you think about it.

"So many times in life you see the end in front of you, but you want to give up. I was taught to keep on going, to try, try and try. If you believe, you create your own reality."