One trick introverts use to become influential public leaders

In 2012, the bestselling author of "Quiet: The Power of Introverts in a World That Can't Stop Talking" took the stage at TED and spoke before an audience of 1,500 people.

You might wonder how a self-proclaimed introvert could assume the persona of a public speaker, especially when her entire work is about being quiet and contemplative in a society that favors entertainment.

The answer is surprisingly simple: passion.

"My book is about the power of being quiet. About the perils of a society that appreciates good talkers over good ideas. And about the terrible pressure to entertain, to sell ourselves and never to be visibly anxious. I believe all this passionately - which puts me in an interesting pickle," Cain wrote in a New York Times essay about having a public persona.

But her own book tackles this question head on.

... we are born and culturally endowed with certain personality traits - introversion, for example - but we can and do act out of character in the service of "core personal projects."

In other words, introverts are capable of acting like extroverts for the sake of work they consider important, people they love, or anything they value highly.

As she explained in the New York Times, "for the sake of a book on the value of quiet, I'm willing to make a little noise."

Cain had a crippling fear of public speaking, which she knew she had to overcome. Passion, she told Business Insider, made it all possible.

"The funny thing is that now I kind of have a career as a public speaker," she said. "I'm speaking about something I'm really passionate about."

Speaking about something you're uncomfortable with is always harder than speaking about something you're passionate about, Cain says. To overcome her fear, she tunes into the energy and drive she gets from knowing that she could be speaking to the parent of a quiet child or an introvert who wants to know how to flourish at work.

"You don't have to be a natural show person to be an effective public speaker. You do have to have conviction for what you're saying," she told Business Insider. "If you have that conviction, it's going to shine through."