Some might call this pedantic, but I think physical reality provided us the earliest idempotency keys, which were natural keys in specific systems. Some effects are idempotent because they address physical reality in a way that converges or provides mutual exclusion. The pigeon-hole principle isn't an instruction guide for birds, it just describes the reality of occupancy. An egg-tooth keeps pecking, escaping at most…
Natural idempotence requires deep understanding of the domain, which developers (and coding agents) do not always have. Also, it's still a limited solution, which doesn't solve the generic case. So it's each much easier to use technical idempotency solutions like: - stamp every initial request / domain event with the UUID (idempotency key) - use client-side IDs instead of using server-generated ones with RETURNING -…
A similar analogy is how 2-phase commit protocols enact (virtual) escrow.