This still comes back to the basic guideline; "learn your fundamentals". You don't need to learn them all (designing CPU instruction sets??), but you do need to

This still comes back to the basic guideline; "learn your fundamentals". You don't need to learn them all (designing CPU instruction sets??), but you do need to know the primary layers you interact with. A web programmer generally doesn't need to be aware of the machine code generated by his application, but should be knowledgeable in networking (layer 3 and up), caching, databases, and so on.