Switching technology is easy, switching domain is hard. You can't specialize in a technology, that is just nonsense, you specialize in a domain.
Or several domains if they are simple enough. Like, the typical needs of a web product are simple enough that you master how to do the database, back end and front end. You wont be able to do the back end or database at Google scale, but you can master doing them at typical scale and I'd actually argue that Google scale is a different domain entirely with a different set of skills, you need a different specialist to handle that problem and he wont be able to efficiently solve your small scale needs either.
I think one person can understand the backend at google scale. You shouldn't LARP solving problems you don't actually have (it's stupid to pay those costs, especially when the google state of the art isn't really that good) but you can still understand it.
- Modern hardware realities (nearby network faster than disk they say, memory of all sort slow relative to CPU). My mental model is the good ol' hydrolic analogy, but with molasses. Wires are slow, components are hardly slower. Flash is slower still. Maybe also think of the machines being close relative to length of wires in CPU and mollases properties.
- DB arch and similar. Well, if everything is molasses synchronizations is clearly hard. Rather than think about nifty hacks in isolation, think about what is the "business logic"'s actual expectations of synchronization. Remember financial settlement is the original example solution for this sort of thing, long predating computers.
Or several domains if they are simple enough. Like, the typical needs of a web product are simple enough that you master how to do the database, back end and front end. You wont be able to do the back end or database at Google scale, but you can master doing them at typical scale and I'd actually argue that Google scale is a different domain entirely with a different set of skills, you need a different specialist to handle that problem and he wont be able to efficiently solve your small scale needs either.