Why do changes after delivery cost more than changes during development? — answered by Engineer Saeed Baatiah
Because a change during development touches code still fresh in the developer’s head with nothing built on top of it yet. After delivery, the project must be reopened, the current state re-understood, the change tested so it does not break what now works, and redeployed without downtime. That is why reviewing the design carefully at the first approval stage — before code is written — is the cheapest hour in the whole project.