> Imagine you are sitting in a bunker. You have no idea what people are out there and what are their intentions. You only receive some incoming messages from st

> Imagine you are sitting in a bunker. You have no idea what people are out there and what are their intentions. You only receive some incoming messages from strangers that may contain anything. They can be just random garbage or deliberately crafted messages to confuse you or lie to you. [...] When two propositions arrive into your bunker, "X" and "Y", we have no trusted reference point to figure out which one is supported by the majority of other people. We only have "data in itself" to judge which one we should choose as the main one. What if the true answer is "neither", and both have been forged by an attacker? If he's sitting in a bunker with no contact to the outside, and an attacker can intercept and manipulate his every communication, how can he "estimate how expensive it is to produce an alternative"? Was the difficulty too low because it's a forgery, or because everybody's abandoned that PoW chain? IIRC, Bitcoin's answer to that situation is that somehow word of the correct chain will get to him (perhaps smuggled by a carrier pigeon), instantly invalidating all of the attacker's work. That makes sense in real life, but not in imagined scenarios where there are no alternative communication channels.