Shared Libraries Create Hidden Coupling

Shared libraries often introduce dependencies that are harder to see than they are to manage.

Common logic in one place. Changes propagate everywhere. Duplication is eliminated. In practice, the shared library becomes a coupling point that nobody owns clearly. Services that depend on it cannot evolve independently. A change made for one consumer breaks another. Versioning becomes a coordination problem that slows every team touching the library.

The cost is not in the library itself. It is in the implicit contract it creates. Every consumer is coupled to every decision made inside it, including decisions made for someone else's use case.

Before introducing a shared library, the better question is whether the duplication it eliminates is actually worse than the dependency it creates. Often it is not. Copied code with clear ownership is easier to reason about than shared code with diffuse ownership. The coupling is the cost, and it compounds.