The Tesla CEO went on and on about how difficult it is to design a robot, including considerations like wear and tear, achieving dexterity with the robot’s hands, and making sure it doesn’t break down. Musk also stressed that it would be difficult to produce the robots.

A month ago, Elon Musk was crowned the world’s first trillionaire after a record public offering for SpaceX. Now investors are growing impatient with the pioneering businessman as the bills come due on his most ambitious promises for SpaceX and Tesla.