The No. 1 green flag I look for before hiring anyone—especially a Gen Z candidate: Kind Snacks founder Daniel Lubetzky

When he hires,, the billionaire founder and guest judge of ABC's "Shark Tank," searches for a red flag: the ability to reflect on oneself.

You will grow if you can be introspective. Lubetzky says that if you lack the skill set to do so, it's much more difficult. It is one of those skills that is most at risk in this age of social media, because we fill every free moment with our phones. Those [Gen-Z] who develop self-reflection will perform better than those who do not."

He screens for self reflection by asking you about your past failures, and what you would do differently the next time. The hiring manager can learn more about your thinking process by listening to a good answer.

Lubetzky says that this shows accountability, humility and the ability to learn.

Schedule time for you to talk to yourself

Lubetzky says he had to learn the skill from scratch. He says that learning to be alone and think was "enormously uncomfortable". This is how he knew the skill was important.

You have to deal with things that you don't find fun. "It is much easier to look at another Instagram post. You need to schedule time to talk to yourself," Lubetzky says.

After a few weeks of practice, he began to cherish his time for reflection. Meditation is a way to keep him improving. He gives up his electronic devices, and spends at least 10 minutes alone every day with his thoughts.

He asks questions to himself, such as: What am I going to be when I'm grown up? How did I manage my relationship with my teammates? How do I treat myself? How do I handle myself?

Lubetzky's not the only business leader who places a high priority on introspection. Jerry Colonna, a "CEO whisperer," recommends, for instance, a method he calls "radical introspection." He told Make It that he spends just a few moments each day to try to understand himself, and to get to the bottom of "why I do what I do."

Claire Hughes Johnson, a former Google vice president, wrote that she looks for self-awareness in candidates before anything else in an article published in Make It in March. She listed some signs to help you determine if it's something that needs work:

You don't know what you like to do

Lubetzky says that his self-reflection skills are most useful when he is responding to negative feedback. They enable him to internalize criticism, and to act on it rather than lash out.

Researchers say that receiving feedback alone can improve self-awareness. According to Columbia Business School neuroscientist Juliette Han, asking for feedback is among the best three ways to develop the "underrated skill".

Han explained that the responses will help you "learn something about yourself," such as your impact on others and how they view you.

Disclosure: CNBC is the exclusive cable network for "Shark Tank."

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