Us old people have the idea of peripherals as input (keyboard, mouse) or output (monitor, printer) - but they've all been input/output for two decades or more; and Thunderbolt and friends are much more like an Ethernet network (reliability of Wake on LAN, anyone?) than they are simple point-to-point connections.

Meaning - anything could be the device preventing what you expect to happen, even if it looks like it should be impossible and have nothing to do with it.

HDMI CEC is the bane of my (home theater) existence.

Which device just woke every other device up at 4am?

Which device just shut everything down while I was in the middle of a movie?

And are they the same device?