One press or several
Pressing a lift button twice still registers one request for a lift.
A payment request can reach a server even if its reply gets lost. The app may retry, unsure whether the payment went through. It can attach the same idempotency key to both attempts, letting the server recognise them as one payment and avoid charging twice.
Effect, not identical response
The server’s replies may have different timestamps, but the payment still happens once. Not every action works this way: adding £10 to a balance twice differs from setting the balance to £10 twice. Teams must plan how to handle retries when duplicates matter.