[holgerschurig]

Well, that is totally wrong. And I deduct that you're rather young.

You think Ethernet is 10BaseT, 100BaseT and similar, i.E. Twisted Pair. But original Ethernet was designed for Coax cable, for 1:many connections.

Basically you had one coax cable and run it from computer to computer. At both ends you had a terminator resistor of 50 Ohm. And at the computers you originally had vampire clamps, later T connectors. That was used until for two or maybe even three decades. First only in research, military and university (e.g. where also TCP/IP was originally was used). But later also e.g. for Novell Netware. The Terminator/RG58 cable/Network card with NE2000-clones or 3C359 cards was relatively cheap, so a lot of offices used that with some Novell Netware file server.

Ethernet was designed for many clients, the CD in CSMA/CD means collision detection. With only two clients, you could do some handshake, like with RS485. But with many clients, this can become cumbersome or impossible. So Ethernet decided to detect this, and to let the senders re-send the packets after a random back-off time.

On the https://en.wikipedia.org/wiki/Ethernet after "Shared Medium" you can see a picture of this entirely not 1:1 equipment :-)

[pclmulqdq]

I have actually read the Ethernet standard almost cover-to-cover, but GP was referring to Ethernet in the common use, not the technically-available options that can be tapped if your building happens to be from the 80's (or is a car). Also, at this point, a lot less of the available "Ethernets" can be tapped than you may be thinking.