Larry Kosilla was on his way to the big leagues of finance. After graduating college, he landed a job on Wall Street, trading natural gas commodities at the New York Mercantile Exchange. Money was going to buy him happiness, and, more specifically, expensive cars. But soon, he realized that he didn't actually want to buy happiness. He wanted to do what he loved, which was to be around expensive cars most of the time. So Kosilla decided to forego the hefty paycheck and instead pursue what he was passionate about: washing and caring for cars.

Larry Kosilla, founder of Ammo NYC. Qin Chen/CNBC

"You can't fake enthusiasm," Kosilla tells CNBC. "There's not enough money in the world to fake enthusiasm." He created a website Ammo NYC to sell detailing products online in 2011. From there, he started a business caring for expensive cars.

"Luckily, my girlfriend (now my wife) and my family were pretty cool with that," he says. At first, it was difficult to secure clients. But, after learning more about Kosilla's expertise and passion, a neighbor's father took a chance on him. His excitement helped him succeed. "I just, I really loved cars," he says. "I think everybody sees whether you're enthusiastic or not."

There's not enough money in the world to fake enthusiasm. Larry Kosilla founder, Ammo NYC

He used social media to his advantage as well. With every new client's car, the entrepreneur took photos of his work and posted tutorials online. Now Ammo NYC is a full-fledged business. Each week, Kosilla cares for cars worth millions of dollars, often for CEOs and successful business leaders. For Kosilla, there's no looking back.

"If you're happy and you become the best at whatever you do you, and that can be a garbage man a cabinet maker or a banker or whatever," he says, "if you're passionate, I think people around your customers or clients your friends whoever will see that." Looking back on the Wall Street career that he gave up, the entrepreneur says, "I've been doing this for, gosh, fifteen, sixteen years now and I don't regret it at all."