[arghnoname]

I've done a lot of web work on top of frameworks and have done work on the Linux kernel including a lot of time figuring out the nitty gritty of how the socket calls are implemented. I have a pretty good grip on everything in between because I enjoy knowing as much of the full picture as I can.

I am weak on the hardware level. I know more than most programmers I've worked with, but embarrassingly little when talking with actual hardware people. I've done a little work to rectify this, but have miles more to go and I'm not sure if I'll bother.

I don't consider myself extraordinary in this regard, so people who know the stack at some level of depth is not all that surprising. I take it as a given that there are many people who know what I know plus hardware. Completionists aren't unicorns (at least not for any sane definition of it. No one knows a modern operating system 100%, for instance).

That said, knowing what the kernel does with sockets is not very helpful for writing a web page. In my experience the vast majority of benefit one gets from being 'full-stack' is knowing one level deeper than whatever they are working on.

If you are writing a performant web server it absolutely helps to know what the kernel does and if you are writing a web language framework you probably ought to understand how the web servers you rely upon generally work (for instance, threading models, etc). You usually don't need to know two levels deep very well and almost never three levels deep. Usually the intervening abstractions are complete enough that those details eventually get papered over into something else.