So I was intrigued by the idea that there's an easy way to prepare a thoughtful, genuine to answer to the question.
It's called the "friends test," and it comes from Simon Sinek, who is a leadership expert and the bestselling author of multiple books including, most recently, "Leaders Eat Last." Sinek has made a career largely out of helping people and companies find their "why," or their purpose.
When he visited the Business Insider office in July for a Facebook Live interview, Sinek explained how the "friends test" can help you find your "why" - and how you can use that knowledge to sell yourself at the beginning of a job interview.
Here's how it works.
Step 1: Pick a friend who you love and who loves you. You can't choose a family member or a spouse.
Step 2: Ask that person, "Why are we friends?"
Sinek said that person will probably be weirded out at first because you're asking them to put complicated feelings into words. So change up the wording: "What is it about me that I know you would be there for me no matter what?"
Then your friend will probably start describing the qualities of any friend: "You're funny" or "You're loyal." So you'll have to push them to describe you specifically.
"Eventually," Sinek said, "they'll give up and they'll stop describing you and they'll start describing themselves" - how you make them feel and the value you add to their lives.
For example, Sinek said his friend told him: "I can sit in a room with you and feel inspired; I don't even have to talk to you."
Ideally, you'll do this exercise with multiple friends, so you can synthesize their responses into one compelling answer.
As for Sinek, he would tell the interviewer:
"I wake up every single morning to inspire people to do what inspires them. … I imagine a world in which the vast majority of people wake up inspired to go to work, feel safe when they're there, and return home fulfilled at the end of the day.
"And I think that your company is devoted to that cause as well, which is why I want to work for you. … I've met people here and they all seem on that path, which is why I feel compelled to interview here. I want to be a part of whatever it is you're doing because I think it'll help me fulfill my own purpose and my own cause."
Watch the full interview: