The prevailing belief is that moving people between projects accelerates learning and spreads best practices, but the hidden cost is a gradual erosion of tacit knowledge. When a developer leaves a codebase, the undocumented shortcuts, the rationales for architectural quirks, and the informal test‑coverage gaps disappear with them, forcing the new owner to reinvent decisions that had already been vetted. Over time the team’s velocity graph flattens not because the work is harder, but because every sprint begins with a hidden onboarding sprint.

At a well‑known music streaming service, a senior backend engineer was shifted to a new feature squad after a year of stewarding a core payments module. Within weeks the module’s incident rate spiked as the newcomer chased down “why‑we‑did‑it‑that‑way” questions that had never been written down. The manager responded by rotating the engineer back, only to repeat the pattern with another teammate, and the cycle of interruptions stretched the release cadence.

The deeper problem is a feedback loop: the more often roles rotate, the less incentive any individual has to document, because ownership feels temporary. That lack of documentation then justifies the next rotation, perpetuating the slowdown. Breaking the loop requires a deliberate pause in movement and a concrete signal that knowledge transfer is complete before anyone shifts.