What does '' failsafe '' mean?
https://youtu.be/cd4Xcc617S4?t=368

Veja uma tradução

Think of "failsafe" like a back-up power generator that turns on automatically when the power goes off. If something fails, then another thing happens automatically to counter it.

For example, on the subway, the driver must push down on a handle for the train to move. This is a failsafe. If the driver becomes ill and lifts up his hand, the train comes to a stop WITHOUT anyone doing anything.

The key to a failsafe is that it has to happen WITHOUT intervention. In other words, if the power fails and someone has to flip a switch for backup power to come on, then that is NOT a failsafe. (What happens if that person is not there?)