What does it mean that granularity is a choice not a discovery?

You choose how finely to decompose based on your purpose — not on some inherent "correct" level of detail. The same material supports different grain sizes for different uses.

Example: You read a 300-page book on decision-making. For your personal note system, you extract 40 atomic ideas — one per note. For a team presentation, you compress those into 5 key principles. For a tweet, you distill it to a single sentence. None of these is the 'right' granularity. Each serves a different purpose: retrieval, teaching, and broadcasting. The book didn't come pre-sliced. You cut it to fit what you needed it for.

Try this: Take one note or document you've already written. Decompose it at three different levels of granularity: (1) a single-sentence summary, (2) three to five key claims each as a separate note, and (3) a fine-grained breakdown where every distinct assertion gets its own card. Compare the three versions. Which one would you reach for when writing an essay? When making a quick decision? When teaching someone? Label each version with its purpose.