Tesla's robotaxi event was long on Musk promises. Investors wanted more details.

For a businessman who perpetually struggles with broken promises, Elon Musk gave himself quite a to-do list Thursday night at Tesla's long-awaited Hollywood unveiling of its driverless robotaxis. His slew of announcements during a 20-minute presentation were short on practical details, which pushed the stock to close nearly 9% lower at 217.80 on Friday. After traversing the fake streets of the Warner Bros movie studio set in a sleek, silver two-door "Cybercab" prototype, he promised that the company's popular Model 3 and Model Y vehicles would be able to operate without driver supervision in California and Texas by next year.