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I think they’re saying that e.g. you shouldn’t index a natural key unless you know that you’re going to search/collate by that key as a column. Telling the database that a certain column contains (a component of) the primary key is adding a restriction to that column.
Other way around, actually; C was one of several languages proposed to model UNIX without having to write assembly on every line, and has steadily increased in abstraction. Today, C is specified relative to a high-level abstract machine and doesn’t really resemble any modern processing units’ capabilities.
Incidentally, coming to understand this is precisely what the OP meme is about.