Nagle's algorithm matters because the abstraction that TCP works on, and which was inherited by BSD Socket interface, is that of emulating a full duplex serial

Nagle's algorithm matters because the abstraction that TCP works on, and which was inherited by BSD Socket interface, is that of emulating a full duplex serial port. Compare with OSI stack, where packetization is explicit at all layers and thus it wouldn't have such an issue in the first place.