There's a moment that comes all too often when I interview entrepreneurs. When asked to identify their business, they tell me there's not just one. Or two. Sometimes there are even more.

Take Stephen Goldmann, a principal in the San Francisco-based food-and-restaurant consulting business the Culinary Edge. He's also a co-founder of Starbird Chicken, a chicken shack financed by the Culinary Edge's venture fund. And he's a co-founder of and an investor in Mindful Meats, an organic beef company, and a partner in Seed + Salt, an organic vegan restaurant--which Goldmann and his partner, serial entrepreneur and marketing guru Mo Clancy, might soon use to launch a packaged-food line.

Yet Goldmann says he's not overwhelmed. "They are all food," he explains. "It feels like I'm not thinking about multiple problems, but one problem and different ways to tackle that."

Reasons for starting multiple businesses vary, from the lure of bringing in income from several sources to the sort of restlessness that drives you to go out on your own in the first place. "Most entrepreneurs I know get bored when a business fully matures," says Jeff Kear, a serial entrepreneur who is now the co-owner of Planning Pod, a web-based event-registration software application. If this sounds familiar, how can you successfully pull off this professional juggling act?

First, make sure all of your entrepreneurial efforts are practically related and take advantage of your existing expertise, so you can easily track how each is doing. "You need to know if you are having a good day or a bad day without giving it a lot of thought," says Stewart Thornhill, the executive director of the Zell Lurie Institute for Entrepreneurial Studies at the University of Michigan.

Many learn this lesson the hard way. Madeline Johnson, a longtime marketing consultant, was running her company out of a New York City co-working space when she realized many of her fellow denizens were eating too much junk food. So she started bringing in home-cooked meals and snacks to sell. "I was making food at 10 p.m. and 5 a.m., but my copy was late and I was missing deadlines," she says. "It was a mess. My health, my relationships, and my other businesses were being compromised--including the one I had had for 18 years."

She walked away from the idea after a six-month trial period, but she still itched to do something new. This time, however, she stuck to what she knew, and set up an online series of classes that teach entrepreneurs about promoting their work. It's a natural extension of her consulting business, Johnson says: "I can take the customers and clients I already have and offer them a new service."

When you own multiple businesses, it's important to remember that no one is an island.
You need to know your limits. Goldmann, for example, always undertakes his entrepreneurial efforts with others, so the business can benefit from each partner's different strengths. In some cases, he's providing the money muscle, while his partner is primarily running the business. "That's the difference between being an entrepreneur and being an investor," he explains.

Finally, don't confuse yourself with well-known billionaire entrepreneurs and gurus like Richard Branson and Elon Musk, who can manage a seemingly limitless number of companies at the same time. "They have their reputation. That's different from trying to bootstrap and hustle a business," Thornhill cautions. "Branson is a holding company that holds companies, and has professionals to run all of them."