Jack Dorsey reveals the most important question he asks when hiring new Square or Twitter employees

Jack Dorsey is a busy man.

As part of the elite group of tech CEOs who have run two companies simultaneously, Dorsey works up to 18 hours a day.

With such a packed schedule, Dorsey likely doesn't personally interview anyone but candidates for top positions at Twitter or Square. But, when he does, there's one question that's most important, Dorsey revealed during a Q&A session on the site Product Hunt.

The question: "Why Twitter?" or "Why Square?"

"I look for passion," he writes. "Only thing that can't be taught."

If he hears "passion for the purpose" in the answer to his question, he'll actually consider a candidate.

"Then I look for leadership and skill," he continues. "Passion and purpose and principles first though!"

Read the rest of the Q&A here.