A secret many small-business owners share with Mark Zuckerberg

"Let's face it," said Mark Zuckerberg to an audience of newly minted Harvard grads during the 2017 Harvard commencement speech. "You accomplished something I never could."

The billionaire Facebook co-founder and CEO meant getting a college degree, and it's a résumé gap that Zuckerberg doesn't share just with Steve Jobs, Bill Gates and other tech visionaries. A majority of small-business owners in the United States don't have a college degree, according to the recent CNBC/SurveyMonkey Small Business Survey. It's hidden fact not often talked about.

Independent business owners without a four-year degree now outnumber those with a bachelor's degree or higher, the SurveyMonkey small-business survey shows. A solid quarter of independent business owners had up to a high school diploma. Add in respondents with associate's degrees or with some college and the number shoots up to 56 percent — more than half of all respondents.

What is the last grade of school you completed?

Did not complete high school	5%
High school or G.E.D.	20%
Associate's degree	14%
Some college	17%
College graduate	26%
Post graduate degree	18%

Entrepreneurs who did not attend or finish college outnumbered those with higher-education degrees across both genders and in every age group included in the CNBC/SurveyMonkey Small Business Survey, except for the 65-and-older category.

Business owners who skipped out on education all shared some common threads: self-reliance, a good idea and a willingness to take risks.

"If you want to get out of college and try to hustle, it still requires a great deal of capacity," said Chuck Runyon, co-founder of 24-hour gym chain Anytime Fitness. He left college after he saw a gap in the market for an always-open gym that focused only on equipment frequently used by members. "I want to make it clear: You have to work every bit as hard, if not harder."

These business owners don't uniformly express a dislike for higher education. In fact, even though less than half of business owners have received a college degree, the 44 percent that have puts them ahead of the general population, where 1 out of every 3 adults has a college degree or more education, according to Census data.

"I loved school and was very passionate about it," said Tanya Jun, owner of Motorcycle Works, an online shop selling custom motorcycle parts and accessories. She dropped out of the University of California, Irvine, when she saw the money was too good to pass up.

"I was a single mother, and the finances were just something I couldn't ignore," Jun said.

More from CNBC/SurveyMonkey Small Business Survey:
Winning the war for workplace talent now requires video
A common hiring fear that no longer makes much sense
Where the country's most confident business owners live

Skipping school can make it difficult to return to the traditional workforce, says Scott Dobroski, a community expert at the careers website Glassdoor. He said most high-demand jobs require a traditional four-year education. "To date we haven't seen conclusive evidence that shows dropouts have a competitive edge," Dobroski said.

Some entrepreneurs advocate for a college diploma despite their success without one. "Continue on, grind it out," said John Bornoty. He founded The Big Salad, a gourmet salad-and-sandwich chain with restaurants in Michigan and Texas. "Sometimes by not having [a four-year degree], I know I got passed over because I didn't have that credential. And whether we like it or not, society likes credentials."

Business owners say a college degree isn't just a symbolic credential; it can offer knowledge to a business founder that could have made their early days easier.

"It was a very hard road," said Amy Freeman, co-founder and CEO of The Spice and Tea Exchange. To create a franchise and secure financing for her company, she had to learn on her own about accounting, marketing and starting a business — and sometimes through painful lessons. If she had received a formal education in business, "I would've known how to build that structure. I would've had resources to tap into," Freeman said.

Mark Zuckerberg dropped out of Harvard to continue work on Facebook, returning this year to give a commencement speech to new Harvard graduates. For entrepreneurs like Zuckerberg, it's not the means but the end that matters.

"An entrepreneurial culture thrives when it's easy to try lots of new ideas," Zuckerberg said. "The greatest successes come from having the freedom to fail."

— By Mike Juang, special to CNBC.com