The first condition for a monetary system is trust. When the money was made of gold, silver and copper, The re was a value in the coin itself. The system, even it was riged many times in the history, by rulers who thined the coins, was more stable and trustworthy. But the big mistake was that they give names and values to those coins, others that their weight and quality. 5 dinars, 5 talers, 5 dollars, or 10 or whatever. In time, economy grows, more money was needed to cover this, but suply of metal was small.

Now, some people has created some plastic money with a certain quatity of gold inside, and the value variable with regard to the grows or decrease of the economy. Maybe, this is the closest to a perfect monetary system.