About a dozen times a year, strangers invite Jeffrey Gitomer to lunch, hoping to ask him for career or business advice.

Mr. Gitomer, a sales consultant, speaker and author, is always happy to help: 'Sure, no problem. I'll even buy lunch,' he tells the entrepreneurs and small-business owners who call. 'But I have a $1,000-an-hour brain-picking fee.'

About half of the people who ask him to lunch agree to his financial arrangement, says Mr. Gitomer, who lives in Charlotte, N.C. 'I think you command respect. And I am worth it.'

Think all divas are women? Or that they are all badly behaved? As a diva might say, 'Wrong, wrong, wrong!'

The concept of the diva originated on the opera stage. But divas (and their male counterparts, divos) are everywhere today: at work, in social groups, in public spaces and even, heaven help us, at home.

Divas, by definition, are high-performing, high-maintenance narcissists. Some are needy, demanding, negative -- and talk almost incessantly about themselves. Researchers say these are 'unhealthy divas' and the source of their narcissism usually is low self-esteem: They are constantlytrying to pump themselves up.

Yet, believe it or not, researchers say some divas are healthy. They adore the limelight and work hard to be always front and center -- but they are willing to make room for others. They are spirited, fun and positive. Because they assume everyone around them is interested in them, they share a lot of themselves -- and in this way bring people together. They have the ability to help others enjoy things that aren't normally enjoyable, whether it's a long line at the store, an office meeting or dinner with the boss.

'Having a healthy diva around brings a lot of sparkle,' says Meredith Fuller, an Australia-based psychologist. 'They make your world more interesting and pleasurable because you can bask in their spotlight with them.'

What separates a healthy diva from an unhealthy diva is this: Healthy divas stand up for others, not just themselves, says Ms. Fuller, author of a recent book about overcoming 'mean girls' and nastiness at the office. 'They are confident of their abilities and contributions, and they love recognition -- but they are happy to give credit to others, too.'

All divas are talented and feel a sense of entitlement. They aren't reluctant to tell their spouse exactly what they want for their birthday or to ask for a raise.

Healthy divas, though, are self-aware. Their sense of privilege comes from their knowledge that they are worth it. They deliver 150%. They know that it's important to say, 'This is what I do well. This is what I deserve. This is what I expect in a relationship,' Ms. Fuller says.

Dan Nainan, a 31-year-old comedian in New York City, says he became more assertive and inflexible a few years ago, after reading a newspaper interview with a call girl. 'She said that when she charged $500, men treated her like dirt, so she upped her price to $3,000, and now men treat her like gold,' he says. 'That really opened my mind.'

Another big influence, Mr. Nainan says, was one of rock music world's original divos -- David Lee Roth, who famously put a clause in the concert rider for the band Van Halen banning brown M&Ms backstage. (It was a safety measure, the singer has explained: If brown M&Ms appeared on the catering table, he knew the concert promoter hadn't read the rider, which gave detailed instructions for constructing the stage set.)

Mr. Nainan, who entertains at corporate events and weddings, now sometimes channels his inner rock star. He refuses to perform when he isn't paid before going on stage, as his contract specifies. 'If you are the talent, you need to demand what you are worth,' he says. 'I am worth it.'

Researchers believe diva-like behavior has an evolutionary basis. 'Narcissism is an adaptation for dominance,' says Lawrence Josephs, a psychologist and professor at Adelphi University, in Garden City, N.Y. 'It's basically saying that because I am better than you, you should defer or submit. You should know your place in the dominance hierarchy.'

Narcissists, healthy or not, usually do well in the short term. They project status. People usually find them extroverted, confident and charismatic -- at least at first. 'Those are sexy traits,' Dr. Josephs says. 'These people would be seen as impressive rivals or attractive partners.'

But studies show there are long-term costs for unhealthy narcissists. They are hypersensitive, demanding and intolerant of different viewpoints. They often have anger-management problems.

Healthy divas have what may be thought of as charismatic intelligence. Unhealthy divas specialize in what's known as 'Machiavellian intelligence' -- and more often as manipulation. 'The more you get to know them, the less you like them,' Dr. Josephs says. 'So the quality of their relationships will deteriorate.'

Experts say a humble person can learn to be a healthy diva. But there's more to it than just throwing on a power suit and some attitude. According to Ms. Fuller, you need to project confidence through body language and speech. You may want to cultivate a presence, through your posture and personal style, and let your personality shine.

And don't forget: You need to recognize others as well as yourself.

Vickie Austin, a 56-year-old business and career coach in Wheaton, Ill'' dresses to attract attention, favoring vintage clothes, pearls and red lipstick. She asks people who want to network or solicit her advice to come to her office -- and bring coffee. Several years ago, after her mother died, she moved to Paris for a month without her husband or son. 'It was a dream I'd postponed for marriage, and I was emphatic that I was going to do it,' she says.

Ms. Austin considers herself a 'respectful diva,' so last month she invited about 20 people, including her accountant, her assistant, her social media consultant, her Web and graphic designers, her tech guy, her intellectual-property lawyer, her aesthetician, her hairdresser and her best friend/yoga instructor to an event she dubbed her Posse Appreciation Luncheon at a local French restaurant. 'I wanted to acknowledge the people who support me because it all boils down to relationships,' says Ms. Austin, who visited each table and thanked the guests individually for their contributions. 'It felt like the Oscars.'