Passion is everything. You cannot inspire unless you’re inspired yourself.

In 25 years of studying communication, I’ve never met an inspiring entrepreneur who isn’t freakishly enthusiastic about his or her idea. Steve Jobs, one of the most passionate entrepreneurs in business history, may have offered the best definition of passion in one of his last public presentations, in March 2011 (he died that October).

"It is in Apple’s DNA that technology alone is not enough -- it’s technology married with liberal arts, married with the humanities, that yields us the results that make our heart sing,” he said.

Related: Richard Branson on What Keeps Him Going

When turned into a question, Jobs’ statement can have a profound impact on your happiness and success. Discovering your true passion is as easy as asking yourself:

“What makes my heart sing?”

Notice how the answer to the question -- what makes my heart sing -- is a lot different than the answer to the question, “What do I do?” Jobs made computers, but designing tools to help people unleash their creativity made his heart sing.

Your passion is not a passing interest or even a hobby, but something that is intensely meaningful and core to your identity. For me, golf is a hobby. I’m even “passionate” about it. But it’s not core to who I am. It is, however, for Rory McIlroy, who won the 2014 British Open.

When asked to describe his passion for golf, McIlroy said, “It’s what I think about when I get up in the morning. It’s what I think about when I go to bed.” For McIlroy, golf isn’t just a passing interest -- it makes his heart sing.

In December, I was invited to be a keynote speaker at the prestigious LeWeb conference in Paris. LeWeb gathers the world’s most passionate entrepreneurs for several days of sharing information that will transform the world. Backstage I met Ferran Adria, the visionary chef who created one of the world’s most famous restaurants, elBulli.

“What is the one quality that all successful entrepreneurs share?” I asked Adria.

“That’s impossible to answer,” he responded. "There are so many paths to success.”

Adria turned away for a moment and I figured our conversation had come to an end. Then he turned to me and said, “I take it back. There is one thing that all successful entrepreneurs have in common, and that’s passion.”

Related: The Definition of Success, According to 5 Entrepreneur Superstars

“How do you know it when you find it?” I asked.

“Let’s put it this way. When you see a glass of wine, what do you think of?”

“A drink,” I said.

“Exactly. You see a beverage. I see a vineyard. I see an ingredient. I see joy. I see celebration.”

I personally enjoy wine, but it’s one of many things I’m passionate about. For Adria, wine makes his heart sing in celebration.

Several years ago I interviewed Chris Gardner for one of my books. He’s the man portrayed by actor Will Smith in the movie, The Pursuit of Happyness (‘happyness’ is purposely misspelled in the title. You’ll have to read the book or watch the movie to find out why).

Gardner told me the story of being homeless, spending nights in the bathroom of a subway station along with his 2-year-old son. During the day, Gardner would put on his one suit, drop off his kid at day care and take unpaid classes to become a stockbroker. You can guess how the story ends. Gardner rose to the top of his firm and became a multi-millionaire.

“How did you find the strength, the spirit, to keep going?” I asked Gardner.

“Carmine, here’s the secret to success: find something you love to do so much, you can’t wait for the sun to rise to do it all over again.”

Gardner had discovered a passion -- a role -- that made his heart sing. Have you?

If you haven’t found your passion yet, don’t just “keep looking.” Ask yourself a better question. Ask yourself the one question that will change everything: What makes my heart sing? 

Related: Panera Founder and CEO Ron Shaich: It's Not About Choosing the 'Right' Path, It's About Knowing What Ignites Your Passion.