Uber CEO Travis Kalanick sat down with Thrive Global founder and CEO Arianna Huffington at the Internet Association’s Virtuous Circle Conference to discuss everything from Kalanick’s sleep habits to his views on the world of tech and entrepreneurship.

“I used to think not sleeping was a good thing,” Kalanick said.

An entrepreneur since the age of 18, Kalanick, now 40, said that over the years he’s learned to reframe his values, thinking of his work and life as a “marathon” rather than a sprint.

“Even if you’re a world-class marathoner, you still need to know where your own personal red line is,” he said. “And it’s good to go past that red line sometimes just to see what you’re made of, but you can’t live there.”

Kalanick discussed the culture of “machismo” among tech founders that feeds a “sleep when you’re dead” culture. Knowing your personal “red line” is key to sustaining yourself, he said.

Huffington pointed to athletes as proof: “We claim to be data-driven, but we’re ignoring the scientific data that is unequivocal, that we’re actually more effective, more productive, and more creative when we take care of ourselves.”

Kalanick said, “It’s really interesting how unintelligent we are about such a simple thing.”

Watch the conversation above.

Originally published at medium.com