> You just send the log output somewhere
How?
Via network socket, serial port, parallel port, however the system in question communicates with the world.
If it's an actual standalone deaf, dumb, and blind black box with zero world interaction then you should, at least, have a hardware probe and step debugging capabilities and you can always flash a sign of some kind on some bus or another.
It does not. You just send the log output somewhere (often a different system). If you have a deployment with no logging infrastructure (either local for smaller setups or distributed for large scale), you have a major problem beyond just debugging visibility.