Mark Cuban, entrepreneur and investor on ABC's "Shark Tank," has invested in hundreds of successful companies to date.
In the 1990s, Cuban founded and sold several start-ups that helped him reach billionaire status. And in 2000, he paid $285 million for a majority stake in the Dallas Mavericks. (Under his ownership, the team won an NBA championship in 2011 and is now valued at an estimated $2.3 billion, according to Forbes.)
But, according to Cuban, "the best investment I ever made was investing in myself, first and foremost," he told Men's Health in an interview published Sept. 1.
While Cuban certainly has a strong track record of self-driven financial success, he was often broke in his early 20s. He slept on the floor of an apartment that he shared with six others, frequently came home to his lights turned off and had his credit cards cut.
"When you're first starting, you may or may not have a job. You don't have any money. You [have] complete uncertainty about your career," he told Men's Health. But "what I learned early on is that if I put in the effort, I can learn almost anything."
It took Cuban a "long time," he said, "but by putting in the effort, I taught myself technology. I taught myself to program."
Cuban started the learning process by landing a sales gig at computer company Your Business Software, despite not having any relevant experience. "I was scared," he wrote in a 2007 blog post, "because I [had] never worked with an IBM PC in my life."
"Every night I would take home a different software manual, and I would read them. Of course, the reading was captivating. Peachtree, PFS, DBase, Lotus, Accpac … I couldn't put them down," he continued. "Every night I would read some after getting home, no matter how late. I had also spent time on the store's computers learning how to install, configure and run the software. People started really thinking I knew my stuff."
The gig paid Cuban $18,000 a year, but by learning these skills, he was able to add thousands of dollars to his commission and land side jobs helping customers with their tech problems.
Although it was "painfully time consuming," Cuban recalled to Men's Health, "that investment in myself has paid dividends for the rest of my life."
Learning about software and programming helped him survive his job at Your Business Software, but "most importantly, I realized that I loved working with PCs," he wrote in his blog.
Cuban ultimately got fired from the sales gig for closing a deal without approval from the CEO, but the job led him to start his own computer systems company, MicroSolutions.
MicroSolutions would go on to make Cuban a millionaire. In 1990, he sold the company to CompuServe for $6 million. Five years later, he and a friend, Todd Wagner, started Broadcast.com, which was acquired by Yahoo in 1999 for $5.7 billion in stock.
"The fact that I recognized that learning was truly a skill, and that by continuing to learn, to this day, I'm able to compete and keep up and get ahead of most people," Cuban told Men's Health.
"The reality is, most people don't put in the time to keep up and learn. That's always given me a competitive advantage."
Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."