There's a good measure of serendipity in the building of any great fortune. But there aren't many billionaires who own the unlikely nature of their success as fully as Craig Newmark.

Speaking at the Inc. Founders House in Austin on Sunday, the Craigslist founder related how, at virtually every turn, he ignored basic business logic and eschewed opportunities to maximize the size and earning potential of his classified ads company. (The Founders House is the inaugural event of Inc.'s Founders Project, an initiative pairing prominent mentors with early-stage entrepreneurs.) That Craigslist has continued to thrive for 24 years and counting--spanning several generations of the internet--is a testament to the soundness of his core philosophy, which is about not trying to do too much. 

It was about a year after Craigslist's founding in San Francisco that Newmark encountered one of his first major decisions: what to name it. "I was going to call it SF Events, because it was a very literal name, and I'm a nerd," he said. "But people around me told me they were already calling it Craigslist because I'd created a brand. And then they explained what a brand was." 

Investing heavily in early growth to lock in market dominance is the strategy of pretty much every venture capital-backed startup. But Newmark, who copped to harboring "a stereotypical engineer's prejudices about advertising," didn't want to do a lot of consumer marketing. About five years into running Craigslist, he tried running a couple of ads for it, but quickly decided it didn't feel right. "Aside from that, it's been purely word of mouth," he said. "Word of mouth, and then more word of mouth."

Nor did he want to ask Craigslist's users to look at banner ads. "They slow the site down, and they strike me as kind of dumb," he said. "So I decided no ads like that, no advertising in any conventional sense." Amid the dot-com gold rush of the late 1990s, leaving easy revenue on the table struck a lot of people as downright bizarre. "VCs and bankers would talk to me and tell me I could make a huge amount of money doing the usual Silicon Valley thing," he said. "But I was a nerd, and I realized I wouldn't know what to do with a billion dollars." 

Despite his reluctance, Newmark has had to figure it out: Forbes officially declared him a billionaire in 2017 on the basis of the value of his controlling ownership stake in Craigslist. His response to becoming fabulously wealthy has been to channel his energy into philanthropy, with much of his support going to military veterans, journalism, and ethics in technology and programming. On the latter score, he believes the biggest tech companies are making progress. "My peers are starting to take some responsibility, at Microsoft, Google, and elsewhere," he said. "They're starting to think about right and wrong in terms of their work." 

He credits his own ethical orientation to "what I'd learned in Sunday school from Mr. and Mrs. Levin, to know when enough is enough." For Newmark, enough was enough almost from the beginning, allowing him to embrace all of his unconventional impulses, from saying no to advertising to firing himself as CEO in order to focus on customer service. "Even at the beginning of doing Craigslist, I realized I would make more money than I needed for myself or even for my family and friends," he said. "That's not an altruistic or noble decision. That's just my value system."