Interfaces Are Where Systems Break

Most failures do not occur inside a component. They occur at the boundary between them.

One part of the system assumes data is valid. Another assumes it has already been validated. A third assumes it is complete. None of these assumptions are enforced consistently.

The failure is not in the components. It is in the gap between them.

Interfaces are where intent is transferred. If that intent is not explicit, the system fills in the gaps with assumptions. Those assumptions rarely align.

Systems do not break because components fail. They break because assumptions do.