Tony Xu , cofounder and CEO of food and grocery giant DoorDash , doesn’t sugar coat the company’s efforts, and challenges, developing autonomous delivery technologies.

“Candidly, it’s mostly been filled with lots of pain and suffering,” Xu said in an on-stage interview on Monday at Fortune ’s Brainstorm Tech conference in Park City, Utah.

DoorDash has been working on autonomy and robotics technology since about 2017, Xu said in what he described as a “long journey.” Any company trying to get involved in autonomous technology and do it at scale must master a variety of different skills, he said: “Imagine learning a new sport, but that sport has five different subdomains just to say that you’re a rookie at that sport.”

You have to build the hardware, develop the software, and fine-

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