alt Hacker NewsThe point of idempotency is safe retries. Systems are completely fallible, all the way down to the network cables.
The user wants something + the system might fail = the user must be able to try again.
If the system does not try again, but instead parrots the text of the previous failure, why bother? You didn't build reliability into the system, you built a deliberately stale cache.
"Idempotency" feels like "encapsulation" all over again.
Take a good principle like 'modules should keep their inner workings secret so the caller can't use it wrong', run it through the best-practise-machine, and end up with 'I hand-write getters and setters on all my classes because encapsulation'.