I had multi-day bugs caused by people not knowing what "0.0.0.0" IP address is, or network address in IPv4 in general, and using that expecting to be connected

I had multi-day bugs caused by people not knowing what "0.0.0.0" IP address is, or network address in IPv4 in general, and using that expecting to be connected to localhost (turns out, when you tell system to connect to any address, there's no guarantee you connect to 127.0.0.1)