When One DTO Breaks Everything: The Cascading Failure Pattern Every Codebase Faces

Sharing a single DTO across multiple architectural layers creates dangerous tight coupling that triggers cascading failures throughout the entire codebase. A simple field rename that seemed harmless explodes into broken controllers, services, tests, and frontend code simultaneously, revealing a critical design flaw. This anti-pattern appears in every tech stack—Java, TypeScript, Python, C#, Ruby, PHP—proving that the problem lies in architecture, not implementation.