Find every write flow in my app that changes more than one record and wrap it in a transaction. Look for the money paths first: checkout (create order, create line items, decrement inventory, record payment), account changes (transfer ownership, merge records), signup (create user, create profile, create default settings), and anything with a loop of inserts. For each flow: wrap the whole sequence in a database transaction so either every write commits or none do. Check my database's transaction support and use its real API (multi-document transactions in MongoDB, BEGIN/COMMIT in SQL, or my ORM's transaction wrapper). Make sure errors inside the flow trigger a rollback and surface a clean failure to the caller, not a swallowed partial state. Keep transactions short: no email sending, API calls, or slow work inside them, since held locks block other writes. Do not wrap single-record writes pointlessly. Do not change the business logic or the order of operations, just the atomicity. Deliver: each flow identified, the transaction added, and a failure-injection test for the money paths: force the second write to fail and confirm the first write rolls back instead of leaving an order with no line items or inventory decremented for an order that doesn't exist.