We've entered an economic era where working a single 9-to-5 until retirement with a growing 401k is no longer the norm. This type of slow growth to the top is actually considered a poor wealth-building strategy. But in the world of entrepreneurship, it's also no longer the norm to build and launch just one business. Today's entrepreneurs are focused on diversifying their companies and income streams, and aren't afraid to fail and try again.

I sold my own profitable company and diversified my income streams with consulting, as a silent partner in startups, and by launching a SaaS business. The best part of diversifying is that you can pivot and grow without risking your entire cash flow. But it's not always easy knowing where to start.

Listening to people and figuring out how I can help - and studying the success of others - helps inform my next move. Here are 10 smart entrepreneurs from different industries and walks of life who can teach you something about growing multiple income streams.

1. Warren Buffett

Warren Buffett is perhaps the smartest, most diversified entrepreneur of our time and holds ownership in over 40 companies. This doesn't account for his personal stock picks, investments, and other money-making endeavors. With a net worth of over $67 billion, it's a safe bet to look at what Warren Buffett is doing to help shape some of your own business practices.

You don't have to strive to be a billionaire to benefit from growing multiple streams of income. You just need a strategy that builds diversification to help boost your bottom line while protecting your interests. If one project goes belly-up, you know the other three you're working on could succeed.

2. will.i.am

William James Adams made a name for himself as producer willl.i.am from the Black Eyed Peas. But instead of retreating into obscurity and popping up to collaborate on a few tracks once in awhile, Adams went on to produce music for Rihanna, Usher, and Britney Spears, to name a few.

Adams also became a renowned tech entrepreneur, and is a founding stakeholder in Beats Electronics with fellow music industry giant Dr. Dre. Beats was purchased by Apple in 2014 for over $3 billion. Today, Adams is venturing into wearables, with the launch of the ill-fated Pulse and the new Dial smartwatch. He's proof you can pivot from one industry to the next and still find success by melding your talents, experiences, and connections.

3. Sara Blakely

Sara Blakely didn't just disrupt an industry, she reinvented the idea of shapewear and ended up a billionaire. Her company, Spanx, is still 100% owned by Blakely, who became the youngest self-made female billionaire in America. Blakely also bootstrapped and managed the early days of Spanx herself, from patent research to marketing, fulfillment, and sales.

Blakely's idea was born from necessity when she cut off the feet of her pantyhose to wear under her clothing to help create a smooth silhouette. She could have just stopped at her first successful product launch. But she continues to grow her line with leggings, maternity, hosiery, and lingerie.

4. Steve Chou

Steve Chou has steadily built a name for himself as that guy who still had a full-time job while running an e-commerce store, a digital course on how to emulate his success, a blog, and a podcast. His website, MyWifeQuitHerJob.com, gives actionable advice on how he and his wife researched product ideas, found manufacturers in China, set up their store, and continued to scale.

Chou recently reported in an income report that he expects to exceed seven figures just from his website. And he finally did decide to quit his day job and focus on his digital empire instead.

5. Limor Fried

In 2005, MIT hacker and engineer Limor Fried wanted to build an online gathering point with her site Adafruit, where people could learn electronics. She grew a multi-million dollar company from selling and teaching how to best use DIY electronics kits. Fried enjoys a cult following of open-source hardware junkies who are passionate about her approach. For starters, Fried offered a $3,000 prize to whoever could successfully hack Microsoft's Kinect.

Fried could have just stopped at writing a blog showing how to hack electronic kits, selling her tutorials, or offering a few DIY kits. But instead she focused on the response of her audience and listened to what they wanted. Adafruit has expanded to selling 3-D printing products, software, and toolkits.

6. Dustin Moskovitz

Facebook co-founder Dustin Moskovitz and fellow colleague Justin Rosenstein were looking for a way to streamline project management and collaboration at the social media headquarters, and Asana was born. The project management tool was originally created as a way to foster teamwork while eliminating reliance on email.

Moskovitz and Rosenstein developed Asana for Facebook's engineering teams. However, it soon became a favorite tool company-wide and was quickly adopted. They realized other companies and entrepreneurs could benefit from Asana too. Moskovitz was smart to focus on what Facebook needed to stay organized and succeed, and deliver on that first internally - and then in a welcoming marketplace.

7. Jilliene Helman

Jilliene Helman started Realty Mogul when she saw the SEC was focusing on crowdfunding and working towards passing legislation to enable it. Helman, always an entrepreneurial spirit, decided to focus on building her own crowdfunding investment site for the real estate industry.

Helman was already making her own profitable investments in real estate as an income stream, and a friend offered to put up $50,000 in whatever investment she selected. This prompted Helman to focus on launching a platform that allowed accredited investors to crowdfund commercial real estate investments with as little as $5,000. To date, 80,000 investors are registered on Realty Mogul, and $220 million has been invested into debt and equity transactions.

8. Richard Branson

Entrepreneur Richard Branson's diverse brand is dizzying, and encompasses over 400 companies under the Virgin umbrella. The Virgin brand first started as a mail order record business, followed by a recording studio that signed name brand acts like the Sex Pistols and the Rolling Stones. Branson focuses on offering something distinct to surprise and delight customers, such as his venture into consumer space flights.

In its early days, Virgin was criticized for being too diverse and distracted from its core business. But Branson says that success and experience can be applied across multiple businesses to replicate the process. That's true whether you're running a billion dollar corporation or adding digital products and consulting to your own portfolio. Focus on what's working, and how you can integrate that into your next venture.

9. Laurel Touby

Journalist and investor Laurel Touby started her career in advertising before starting Mediabistro. In the company's infancy, Touby threw cocktail parties to meet other media pros, and turned her growing connections into a job and networking website. She's a prime example of how building the right network can lead to that network becoming customers for your business.

Mediabistro started with job information and media articles, and grew into a multi-million dollar company hosting digital courses, workshops, and premium content. Touby sold Mediabistro for $23 million and later took the helm as Managing Director of the seed investing firm Flatiron Investors.

10. Neil Patel

Content marketing expert Neil Patel started his first entrepreneurial pursuit in high school when he sold burned music CDs and cable black boxes to his classmates. Patel focused on analyzing why services and companies were successful and trying to replicate the success, then filling in the blanks along the way. At one point, he even built a site called Advice Monkey to emulate Monster.com's success, but realized he had little opportunity to monetize it without the ability to accept credit card transactions.

Patel kept growing his income streams with hits and misses before landing a $3,500 consulting gig on internet marketing. He landed the gig after giving a speech in his college class on how search engines work. He grew that success into multiple companies, including Crazy Egg, Hello Bar, and KISSmetrics.

Who makes your list of smart entrepreneurs with multiple income streams? Let me know by leaving a comment below: