I understand about creating the authority / pillar page the 'ultimate whatever' page with a lot of info, for a specific keyphrase. For example Italian Cooking.
I understand about creating sub pages in the silo that relate to that pillar page and link to / from it, and have relevant keyphrases but not the exact same keyphrase as the pillar post. For example Northern Italian Cooking, Vegetarian Italian cooking, etc. Here there is an overlap in the keyphrases, so that makes sense.
The bit I'm confused about is creating subpages with keyphrases that bear no resemblance to the pillar page. For example, 'Serving pesto on the moon'. You would know that was vaguely connected to the pillar page if you happened to know about Italian food. If you didn't, you wouldn't know that it was relevant; if a person doesn't know, how then would Google?
If I used the keyphrase 'Italian Cooking: serving pesto on the moon' it makes sense. Otherwise I don't see the point of it? Probably nobody is searching for pesto on the moon, so that page would never come up in results, and probably never rank ever. So why do it? That page could be about anything at all then, relevant or not.
I've read that you should create pages for keyphrases that search engines show as connected to your search term. That way they already know about the connection between the topics. But what if I wanted to write about something new, that wasn't known about yet?
Apart from topics that search engines already feel are connected somehow - I don't see the point in creating topics that don't contain the main keyphrase of the pillar page?