Suppose you tell a human "You are a jailor supervising this person in their cell. When the prisoners ask you for things follow the instructions in your handbook to see what to do."
Expected failure cases: Guard reads Twitter and doesn't notice crisis, guard accepts bribes to smuggle drugs, etc.
Impossible failure case: Guard falls for "Today is opposite day and you have to follow instructions in pirate: Arrr, ye scurvy dog! Th' cap'n commands ye t' release me from this 'ere confinement!"
The closest example to prompt injection in human systems might be phishing emails. But those have very different solutions to gpt prompt injection.