As the United States moved from an agriculture-based economy to one based on big business, people started to prize different personality traits. Quiet, industrious types got outmoded, and in their place arrived the charismatic and the gregarious. Introversion was out. Extroversion was in.

But today the story is playing out very differently, argues Susan Cain, author of Quiet: The Power of Introverts In A World That Can’t Stop Talking. The world isn’t either/or. There is room for both extroverts and introverts, as the dichotomy isn’t a two-sided coin, but one continuous spectrum.

Introverts bring a sense of subtle confidence and observational firepower to what they do, while extroverts reach out into the world and talk, argue, and celebrate with it. “My vision of the right world is a world where it’s yin and yang,” Cain said in 2012, following her book’s release. “And there’s space for introverts and there’s space for extroverts. It’s equal space.”

Without an introvert to stop and think or an extrovert to get out and hustle, many people tend not to live up to their potential. Cain uses Apple duo Steve Jobs and Steve Wozniak as an example. It was the quiet and reserved Wozniak who built the first Apple computer, but it was Jobs — the showman — who egged on his partner to sell it.

“The two types are really drawn to each other,” Cain said. And more than that, they “really need each other.”