What is zettelkasten method?

Example: A product manager writes her first atomic note: 'Users abandon onboarding at step 3.' It is clumsy — it contains a claim without evidence, no link to supporting data, and a title that could be more precise. Six months later, her atomic notes look different: precise titles, sourced claims, explicit links to related notes. She did not follow a rule that made this happen. She practiced decomposition hundreds of times, each iteration slightly better than the last. The note she writes on day 200 would be unrecognizable to the person who wrote that first one on day 1 — not because she read a better guide, but because the skill of atomicity developed through use.

This concept is part of Atomicity and Decomposition in the How to Think curriculum.