Aman Behal’s automated robotic arm functioned perfectly. Outfitted with sensors that could “see” objects, grasp them with enough force to hold but not crush them, and return them to the user, it easily outperformed the same arm under manual control on every quantitative measurement.

Except one. The arm’s users — patients with spinal cord injuries in an Orlando hospital — didn’t like it. It was too easy.

“Think about the Roomba,” Behal told Wired.com. “People like robots, and they like them