Not everything can be idempotent, nor immutable, nor stateless. But if you adopt the core assumption that you will achieve those states in the places where they can be achieved (and attempt to make them easily achievable with patterns that support them), then when you do isolate situations that cannot be, like physically shipping a product, you can pay more attention to to making them correct. Most of the innumerable in memory, business logic, database operations, etc., behind the shipment can be made idempotent, which gives you more confidence that you didn't trigger a physical shipment because of an issue.

In other words, the decision to ship can be made idempotent. And that, in a modern software app, the result of a pretty complex set of things that can individually go wrong.

You could argue that Amazon made themselves something of a success by bringing at least the principle if not the actuality of idempotency to the shipment itself. By making it easy to get a replacement shipped.