In start-up lingo it's called "stealth mode" — where founders keep their business secret, sometimes to keep information from competitors, sometimes as a marketing strategy. But in the '90s, Sara Blakely hid her fledgling shapewear company Spanx from even those closest to her for a different reason.
"When I started Spanx," Blakely said in a LinkedIn post on Thursday, "I kept the idea from my friends and family for a year knowing that out of love, they might prevent me from taking a risk."
Blakely only discussed her business with the people she needed to bring Spanx to market, which was her patent lawyers and manufacturers.
"[I]t was just a gut feeling I had to keep it to myself, because I believe that ideas are the most vulnerable in their infancy," she said on a September 2016 episode of "How I Built This." "And it's instinct to turn to your right or left in that moment and tell a friend or tell your husband."
Blakely said she did not want to share her idea because once she did, "instantly ego's invited into the mix."
"Then you end up spending all your time defending it, explaining it and not pursuing it. So I needed to be at the place where I knew I wouldn't turn back no matter what I heard," Blakely said.
With $5,000 Blakely had saved selling fax machines door to door, and no background in design, business or manufacturing, she launched Spanx in 1998.
"I was working on my idea at night and on the weekends," she said on "How I Built This," adding that she needed to keep her day job "because I needed the money coming in and the health insurance and all that comes with that."
Once she felt comfortable, having "invested enough of my time and had enough sweat equity into the idea," Blakely decided to tell her family and friends what she had been building.
"And the things I heard were, you know, well, honey, if it's such a good idea, why hasn't somebody else already done it? And well, if it is a good idea, Sara, you know, you're going to spend your savings on this, and then in six months the big guys will just knock you out of the water," she said on the podcast.
"And that was all coming from a place of love. But I feel like if I had heard that the night that I cut the feet out of my pantyhose," she said, referring the moment inspiration struck for Spanx's first product, "I'd probably still be selling fax machines."
Blakely ultimately built a billion-dollar business, giving her a current net worth of $1.1 billion, according to Forbes.
"Believe you can do it, and you will," she said in her LinkedIn post. "Protect your dreams, ideas and goals."
Like this story? Subscribe to CNBC Make It on YouTube!