Not sure if this is rethorical, but it's a great question. In hacker-news-pedantry tradition i will answer: A. A dollar bill represents an accounting entry in

Not sure if this is rethorical, but it's a great question. In hacker-news-pedantry tradition i will answer: A. A dollar bill represents an accounting entry in a bank account. Banks are the third party that facilitate trust and the rules by which 2 actors trade. B. Dollar bills are legal tender for the payment of taxes. They are enforced by government, which is the sole legal arbiter of coercive action. Taxation requires every citizen to hold a reserve of state currency. C. Due to the specialized printing process dollar bills are, at least theoretically, hard to counterfeit. D. Ubiquity as trading mechanism, barter requires double coincidence of wants (rare) or interpersonal credit (lack of third party oversight to guarantee fair play). When holding assets, these can deprecate (or appreciate) in value, and would need to be converted in cash holdings to avoid the impracticalities of barter exchange. E. They are an convenient way of turning digital entries into tangible user objects, since they hardly take any space. I'm sure you could keep the list going. Notice how cryptocurrencies satisfy a lot of those conditions. Also notice how bitcoin in particular fails at a number of them.