Imagine knocking on doors to sell fax machines—then, years later, becoming a billionaire. That’s exactly what Sara Blakely did. The 54-year-old founder of Spanx recently spoke with The School of Hard Knocks, a YouTube channel focused on financial literacy and entrepreneurial content, where she talked about how she built her own company—with money she saved up from years of selling fax machines, and with no outside investors.“I started it with five grand from selling fax machines and self-funded the entire 21 years,” Blakely, currently worth an estimated $1.3 billion, said. “I sat down with myself and I was like, you wanna spend your five grand on a vacation? Or do you wanna try to bet on yourself?”Blakely’s journey with Spanx began in 2000 when she was 29 years old, working as a national sales trainer for Danka, an office-supply company, after spending seven years selling fax machines door-to-door. Her breakthrough moment came from personal frustration: She wanted to wear white pants but couldn’t find the right undergarment to create smooth lines beneath them. Her solution—cutting the feet off control-top pantyhose—became the foundation for what would eventually become a $1.2 billion company.Building an empire without investorsWhat sets Blakely apart from most entrepreneurs was her refusal to accept outside investment. “I never had a single investor in Spanx other than me,” she said. The Florida State University grad started Spanx while still working her day job at Danka, spending nights researching fabrics, patents, and trademark designs. She wrote her own patent application, secured the Spanx trademark for $150, and found a hosiery mill willing to produce her prototype after multiple rejections. But by disallowing outside investment, she maintained total control over her company, and its profits.A breakthrough at Neiman MarcusWhen asked about the craziest thing she did as a business owner when just starting out, Blakely said she had just secured placement for Spanx in Neiman Marcus, but after noticing she was put in a “pocket” in the store’s expansive hosiery department, she bought bins at Office Depot and placed them at every cash register throughout the store—”which is so, so not okay,” she admitted. “Neiman Marcus has a very strict visual department, but everybody thought somebody else approved it,” she said. “So I was trying to get the product out of the sleepiest corner of the store and move it around to where the customers actually were … You do whatever it takes.”Blakely said her unauthorized gamble paid off: Customers began buying the product “like crazy,” and by the time management discovered the placement, the CEO reportedly said, “whatever this girl is doing, let her keep doing it.”“I always say, ask for forgiveness, not permission,” she added.Thanks to Blakely’s efforts—and a timely inclusion on Oprah Winfrey’s “Favorite Things” list in November 2000—Spanx achieved $4 million in sales in its first year, and $10 million in its second year.Strategic entrances and exitsIn 2021, Blakely sold a majority stake in Spanx to private equity firm Blackstone at a $1.2 billion valuation, while retaining a significant equity position and becoming executive chairwoman. The deal marked the end of her 21-year run as sole owner, but bestowed her with billionaire status. (She had become a billionaire years earlier, but her net worth had dropped below $1 billion in 2020 during the pandemic).When asked about her advice for young people aspiring to become billionaires, Blakely said it’s important to motivate yourself and not get discouraged by outside opinions and intrusive thoughts.“In today’s world, ideas are the most vulnerable in the moment you have them,” she said. “I waited a year before I told any friends or family what I was working on, and that’s because I didn’t want ego to have to get involved too early. My family was like, ‘Sara, if it’s such a good idea, why hasn’t anybody already done it? Even if this is a good idea, the big guys will knock you off in six months, and you’ve spent your life savings on it.’ Had I heard those things the moment that I had the idea, I would probably still be selling fax machines.”This story was originally featured on Fortune.com