When Barbara Corcoran interviewed candidates for her successful real estate brokerage, she never bothered to read their resumes first. Resumes can be easily fabricated and perfectly finessed, so she didn't see the point. Instead, she wanted to know one key fact about each potential employee: Was he or she happy or not?

Looking for the light.

The self-made real estate mogul and Shark Tank star cares deeply about personality and drive. That's what she told Adam Bryant, who interviews top executives about leadership for the New York Times's Corner Office column. "When I hire people, I just look for the light in the person, to see what's good about them," she says. "I can spot it a mile away."

Though "looking for the light in people" might sound a little hippy dippy, clearly Corcoran has something figured out. In 1973, she founded the Corcoran Group with $1,000. When real-estate giant NRT Incorporated offered to buy the business 28 years later for $22 million, Corcoran counteroffered and asked for $66 million. She got her asking price.

So it's safe to say Corcoran has a knack for building successful and high-performing teams. And she has one interview question that's her magic bullet for determining if someone will make the cut: Tell me about your family.

Family matters.

Corcoran says she wants to know about a prospective employee's parents. How he or she grew up. How someone speaks about family reveals so much about how that person learned to approach challenges. By the time someone is sitting across from you in an interview, his or her perspective is likely pretty ingrained. "If their family couldn't give them a positive attitude, there's nothing I can do that's going to change it," she says.

She says success all comes down to positivity and happiness. In her experience, unhappy people aren't great performers. Even those who have all the right skills on paper will never reach their full potential if they're unhappy. As the boss, Corcoran observed early on the consequences one grouchy person can have for a larger team. "I learned that if you have just one unhappy person in a pool of 30 happy people, you feel that weight," she says.

She hates complainers. She loved firing them when she was running the Corcoran Group. Corcoran takes a similar approach with her Shark Tank entrepreneurs. She looks for people who are determined to succeed, no matter what. But the very moment an entrepreneur starts playing the victim card, Corcoran doesn't want to hear it.

She even has a dramatic way to move on from complain-y entrepreneurs. When she first signs a deal with any entrepreneur, she displays his or her photo on the wall of her office. But the moment she hears that entrepreneur start playing the victim card, she flips the photo over. "They'll never succeed. Victims don't succeed," she says.