After interviewing billionaires and CEOs, entrepreneurs and scientists for my new book, Five Stars, I’ve concluded that it’s time to stop referring to public speaking as a ‘soft skill.’ A wealthy investor at Y-Combinator, the iconic investment firm behind startups such as Reddit and Airbnb, convinced me to stop using the term. During our conversation, he called out my mistake.

“Let’s talk about a soft skill like storytelling,” I said.

“Soft?” he shot back. “If an entrepreneur can’t tell a convincing story, I’m not investing. You call it soft. I call it fundamental.”

Warren Buffett would agree. He says investing in yourself is the best investment a person can make—and public speaking is the best investment of all. Buffett has put precise cash value on communication. “The one easy way to become worth 50 percent more than you are now — at least — is to hone your communication skills,” Buffet says.

The Growing Value of Changing Minds

In a world built on ideas, the persuaders— the ones who can win hearts and change minds—have a competitive edge. While researching my book, I spoke to economists and historians like Deirdre McCloskey at the University of Illinois. She conducted an impressive research project to prove that old-fashioned rhetoric—persuasion—is responsible for a growing share of America’s national income.

McCloskey analyzed 250 occupations covering 140 million people in the U.S. In some cases, persuasion played a more limited role than others (think firefighters versus public relations specialists). McCloskey reached the following conclusion: Persuasion is responsible for generating one­ quarter of America’s total national income. She expects it to rise to 40% over the next twenty years. McCloskey’s research was taken up by another economist in Australia who reached a similar conclusion.

To understand why persuasion is no longer a soft skill, we need a short history lesson. In 1840, nearly 70 percent of the U.S. labor force worked on farms; today less than 2 percent of Americans work in agriculture. Manufacturing’s share of the labor force has dropped from 40 percent in 1950 to under 20 percent today. Income from manufacturing continues to fall as robots replace workers and artificial intelligence takes over repetitive tasks once handled by humans. The main task of the jobs that are left—and the new ones created—is to change minds. As McCloskey explains, “Nothing happens voluntarily in an economy, or a society, unless someone changes her mind. Behavior can be changed by compulsion, but minds cannot.”

By calling public speaking a ‘soft skill,’ it diminishes the skill’s value in a world that cherishes the ‘hard sciences.’ Public-speaking isn’t soft. It’s the equivalent of cold, hard cash.