The architecture diagram shows clean rectangles. “Stateless API tier,” someone wrote in Lucidchart, then drew an arrow to a managed database. The presentation went well. Everyone nodded. Six months later, after the third incident where a rolling deployment dropped active uploads and the on-call engineer spent two hours discovering that session affinity was secretly enabled in the load balancer config — that’s when you realize the diagram lied.
Not maliciously. But comprehensively.