Łukasz Reszke's wroclove.rb 2023 talk walking through six stories from Trezy, a cash-flow management SaaS: (1) processing open-banking webhooks asynchronously by storing them as technical events before handling; (2) introducing a bank-account aggregate to enforce operation rules and deal with out-of-order webhooks via a stored timestamp invariant; (3) a 'closed bank account with missing events' bug caused by a new feature bypassing the aggregate, fixed by writing a test, backfilling via a migration event, and reinforcing that all writes must go through the aggregate; (4) pending-transactions bug traced by replaying stored events and fixed with acts_as_paranoid soft-deletion quirks; (5) a larger project encapsulating transaction-classification rules in an aggregate, introducing real CQRS-style read/write split and discovering three explicit classification processes which were themselves event-sourced; (6) a tiny subscription-cancellation feedback feature that used a single event + Slack handler and linked to the tenant stream. The speaker introduces the team's pragmatic 'event-driven CRUD hybrid' style, stresses that event sourcing is 'just a persistence pattern', and encourages adopting it gradually in startups and legacy projects rather than waiting for greenfield.