https://arstechnica.com/gadgets/2017/09/apple-says-face-id-didnt-actually-fail-during-its-iphone-x-event/

The first public demo of Apple’s Face ID phone unlocking system didn’t go exactly as planned.

During the company’s big iPhone X reveal this week, Apple software engineering chief Craig Federighi suffered a semi-cringeworthy moment when he was unable to unlock the new handset onstage using the new authentication tech. The device prompted Federighi to use a passcode instead, leading him to switch to a backup unit, which worked properly.