Cryptocurrency
People often use cryptocurrencies to do speculation.  That makes building a system of more or less stable exchange rates very difficult. Another problem is the inequality of distribution: a small number of people have most of the cryptocurrency. For example: about 1.000 people hold half of the total amount of bitcoins in the world.  So if any of these people start using the Bitcoin that they own, they will change the exchange rate. It also means that these people have a great influence on the value of the currency. They can change its value easily. The currency itself only tells you who owns it. Exchange rates of cryptocurrencies are established outside the system. Traders and brokers set the exchange rate. This is not a guarantee that they trade cryptocurrency at the value that they suggest.  The unit of cryptocurrency doesn't have value by itself.