A recent Wall Street Journal article pointed out how often job candidates lie during hiring interviews. One psychology professor conducted studies showing that job candidates tell two to three lies on average during a 10-minute interview.

In a tight job market, the most common way job candidates mislead recruiters is to exaggerate their enthusiasm for the job. After all, no one would say, "I'm only here for the paycheck." Instead, they'll say, "I've always been really passionate about widgets!"

We all want to hire people who are passionate about the job, but how do we know if they're as passionate as they seem? The best interview advice I've heard on the subject comes courtesy of Larry Smith, a popular professor of entrepreneurship at the University of Waterloo. Smith's TED talk on choosing a career path has been viewed nearly seven million times.

Smith told me the best interview question to ask is just one word: Why?

In one word you can learn volumes about a job candidate. It doesn't give people room to hide. It works like this:

Candidate: "Thanks for asking me for an interview. I'm really excited about this job."

You: "Why?"

Candidate: "Well, because I've always been passionate about this field."

You: "We love people who are passionate. Tell me more. Why are you so passionate about it?"

At this point, the job candidate will provide a wealth of information about their true motivation. If they're interested in the job only for a paycheck, they won't have much more to add. If, on the other hand, the role fulfills a life-long passion, they won't stop talking about it. True enthusiasm is hard to control.

A genuinely passionate job candidate will tell you about the books and articles they've read on the subject, the conferences they've attended, and the people in the field who have inspired them. They'll offer detailed descriptions about your product because they're obsessed with it.

Here's how Larry Smith describes the difference for his students.

Interviewer: "Why do you want to work for us?"

Candidate: "I love telecommunications."

Interviewer: "Why?"

Candidate: "Because I use the phone."

A person who is really enthusiastic about the job wouldn't stop there. They would add much more. For example, someone who is deeply passionate about voice communication might say:

"When Alexander Graham Bell invented the telephone in 1876, he could never have imagined where we'd be today. There are dozens of books about him. I've read many of them. My favorite is Reluctant Genius by Charlotte Gray. He had a passion for inventing things like I do. Oh, there's one story about him that I love ..."

Smith says the human mind cannot help thinking about that which it loves. And it can't stop talking about. 

I was thinking about Smith's observation during a recent conversation with Allie Webb, the founder of Drybar, a hugely successful chain of hair salons that provide blowouts. I was interviewing Webb over Zoom about the courage it takes to start a business when others say it can't be done. A hair salon that doesn't cut or color hair didn't seem like a sure thing, but Webb built turned her passion into a $100 million business.

"I love everything about hair," she began.

Webb then talked about hair uninterrupted for the next five minutes. I learned more than I ever expected to know about women's hair. I was smiling the whole time because I've rarely met someone who exudes as much enthusiasm as Webb does. And I all did was ask her why she had decided to start a hair salon.  

"It's nearly impossible to start a company if you don't have a deep love for the product, a passion for it," Webb told me.  

Webb is right. Passion is everything--for business owners and for the employees they hire. Don't make a mistake by hiring a person whose heart isn't in it. Start with why.