Stewart Butterfield has no doubt been called many things over the course of his career. But the blurb that accompanied his No. 88 spot on Vanity Fair's New Establishment List this year included suitable-for-framing descriptions of him like: "The only person everyone actually likes" and "The Unofficial Nice Guy of Silicon Valley."

Could being nice to people be the ultimate leadership hack?

"Maybe sometimes you do have to pound your fist on the table," Butterfield told me during our conversation on 'The Art of Leading.' "But people have kind of unpredictable and often unhelpful reactions when they're fearful. If you create an atmosphere that is filled with fear, then people are not going to make the right decisions most of the time. They're going to act way more defensively than you would want them to act, especially in an environment where you're growing really quickly. You don't want to have them withhold their ideas or withhold their effort and not want to go out on a limb."

As Slack has grown quickly, and as talk builds of a possible IPO in 2019, Butterfield said he has shifted his approach to how he runs his company.

"Three years ago, I would have thought that my job is to be smarter than everyone and to make all of the really important decisions," he said. "And there could be a time at a small enough organization where that's more or less true. But it's not the job when you get 100 people or 500 people or 1,000 people. Starting to understand what the job actually is was a big breakthrough for me because suddenly I realized how to spend my time, which is not thinking super hard about some decision that we have to make but rather setting the strategy and vision for the company."

He added: "It's about ensuring that the performance of the organization as a whole is as high as it can possibly be, and that it is coordinated, aligned, and able to respond to new information. Those are, I think, the most important things."

Butterfield is also unusual in the world of tech CEOs because he studied philosophy in college rather than computer science or computer engineering. But he said the training was invaluable for being able break issues down to their cores.

"Logic and philosophy of mind, and the rigor with which the academic discipline approaches that stuff, is super helpful," he said. "It's about getting to the bottom of arguments and getting to real clarity -- and nothing is clearer or more kind of perfect than logic, because it's just abstract rules. If you can ask yourself, why, why, why, and get to the bottom of what the objectives are, then it can be very clarifying, both for you and ultimately for everyone else."

Adam Bryant is a CNBC contributor and managing director of Merryck & Co., a senior leadership development and executive mentoring firm. A veteran journalist, Bryant interviewed more than 500 leaders for the "Corner Office" feature he created at The New York Times. Parts of this interview were edited for clarity and space.