I remain impressed with all of the people who deal with the physics required to let me pretend that everything in computers is nice and digital.
A few years ago, after grumbling that my Xbox download speeds were low (rarely above 100 Mb/s, even with FTTP and GigE to the router), I discovered that one of the wires in one of the twisted pairs in the cable had snapped a little bit back from the connector. Cutting the end of the cable and popping on a new plug fixed it completely.
With one of the twisted pairs out of action, the endpoints still managed to negotiate a working 100Mb/s connection.
As someone who remembers immense struggles to get 10 Mb/s ethernet working reliably (with coax or twisted pair) in the '90s, this was simply not a failure mode I'd expected. A cable that broken should just stop working, not give me a connection that, for almost all purposes, is completely fine.