> On the other hand, having the wisdom of knowing what can be static in the first place? I don't think that it's something teached.
All traffic is static by definition. You are not modifying bytes when they are in transit to user. And you don't have to serve different bytes each microsecond just because users want to be "up-to-date". The network latency is usually around 40ms or so. If your website serves 1000s of requests per second, you should be able to cache each response for 10ms, and no one will ever notice (today this is called "micro-caching").
Of course, most webpages can't be cached as whole — they have multiple "dynamic" parts and have to be put together before serving to user. But you can cache each of those parts! This is even simpler if you do client-side rendering (which is why MangaDex abysmal performance is pathetic).
Then there are ETags — arbitrary strings, that can be used as keys for HTTP caching. By encoding information about each "part" into a substring of ETag you can perform server-side rendering and still cache 100% of your site within static web-server, such as Nginx. The backend can be written in absolute hogwash of language such as Js or Python, but the site will run fast because most requests will hit Nginx instead of slow backend. ETags are very powerful, — there is literally no webpage, that can't be handled by a well-made ETag.
Even pages, that need to be tailored to user's IP can be cached. It is tricky, but possible with Nginx alone.
Instead of "static" you are better off thinking in terms of "content-addressable".