Chris Hulatt was just 23 when he decided corporate life wasn’t for him. He’d spent two-and-a-half years on Mercury Asset Management’s grad program. It was long enough to meet cofounders Simon Rogerson and Guy Myles, and long enough to know he wanted out.

“Everyone thought we were totally mad,” Hulatt recalled of the moment the three of them dropped out of the coveted grad program to launch Octopus Investments at the turn of the millennium.

They didn’t have a grand business plan or any investors lined up—just $25,000 of Hulatt’s savings, what they now call the “Terminator gene” and zero desire to ever return to the corporate world.

“We thought: ‘Why don’t we have a crack at starting our own fund management business?’ You know, one of those kinds of rash things that people sometimes decide to do,” Hulatt told Fortune.

“We didn’t want to get a traditional job again.”

Hulatt never did have to go back to the 9-to-5 grind for another employer.

Today, Octopus Investments manages more than $13.2 billion on behalf of its clients, according to the company. More than 70% of these funds target investments that tackle climate change, improve people’s quality of life, and address inequality.

And the company is now one of six divisions under the parent company, Octopus Group, which includes the British energy giant Octopus Energy. He’s still co-running Octopus Group which now employs over 14,000 people and serves 11.3 million customers.

Pick up the phone and start dialing

Without their salaries to fall back on, Octopus’s Hulatt and his cofounders had to find investors for the business quickly or face returning to their old jobs with their tails between their legs.

They set up camp in the front room of Hulatt’s London flat with a trusty copy of the Yellow Pages, one landline phone between them and “one ancient laptop which was about an inch thick”.

“We spent much of 2000 calling thousands of people to try to persuade them to invest in this startup fund manager company they’d never heard of run by three very young people who didn’t exactly have a long pedigree in the financial industry,” Hulatt said. “It was super hard.”

“One person held his phone up, and he said, ‘listen to this, this is the noise of my shredder shredding your business plan—never call me again.’

“It would have been all too easy after we’d spent a month or two trying to persuade people to invest in us to just give up and assume we weren’t going to go anywhere,” he added—but they didn’t.

As Wolf of Wall Street‘s Jordan Belfort would say, they picked up the phone and kept dialing.

“It took a long, long time (the best part of all of 2000), but we really wanted to try and make business get up and running.”

By the end of the year, after many noes, the young founders had convinced 85 people to inject around $2 million into Octopus Investments.

It’s a lesson in the power of small wins: It wasn’t a first-of-its-kind idea, an impressive presentation that won over a big VC firm, or even a stroke of luck that got Octopus Investment off the ground and into the success it is today.

“We just kept at it. It’s that kind of stubborn refusal to give in—we call it the “Terminator gene”—that has been so important to us,” Hulatt advises budding entrepreneurs.

“You just have to be totally persistent, totally believe in yourself and never give up.”