His 21 ways bitcoin book is good too, although the majority of chapters isn't written for now.

It's brilliant that virtual markets such as second life, diablo and runescape have had actually real economies, just with a virtual arena, susceptible to dupes, regulatory pressure and so on. Bitcoin being a digital currency and not virtual, because if the arena of runescape is limited to the game, bitcoin's limited to who can store a seed phrase. In order to spend it also requires a computer connected to the internet. That's all.

Fiat's arena is the countries who imposes it. If they fall, their fiat currency falls too.