A slice you can see is a slice you can judge
The reason to ship the thinnest slice is not speed for its own sake. It is that a slice on a screen answers questions a plan never can. You see the type is too heavy, the spacing is wrong, the empty state was never really designed. Until it renders, every one of those is a guess.
So the discipline is not just ship small. It is ship small, then look — and let what you see on the page choose the next slice, instead of a plan written before anything existed.
The list is the second slice looking back
This index is a small example of the idea. It reads the posts that exist, sorts them so the newest is first, and shows each with just enough to decide whether to open it. Nothing about a post is written into the page — add a post file and it appears here on its own.