Gold and Silver are simply attempts to take human weakness out of the picture by tying the concept of money to something that cannot be easily forged or mass produced. This works to a degree but it historically also ultimately fails to restrain us from eventually debasing and destroying the currency system.
This is the most misleading statement about the viability of metals ever. Just because someone attempts to debase the currency does not mean gold or silver has "failed" in any way. It's valued by it's metal content, not anything else. Contrary to whatever lies Armstrong will tell you, when they debased silver by 50% in Rome, the soldiers just asked for twice as much pay, and so did the merchants for their goods. Yes, a king or whoever can sometimes trick people with debasement over a short period of time, but never the long run.
The monetary aspect of metals is valued not by the metal content but by what one can get for the metal at any given time in terms of goods and services in trade.
If a metal based monetary system cannot prevent recurrent debasement of the unit of measurement either via direct physical debasement or via the addition of financial paper instruments then it has failed as a sound monetary system. Metals have repeatedly failed in history though they are superior to paper instruments which fail much faster. The concept that you can retain some value by hiding non debased pure metal via burying it in a hole while the overall currency system and economy implode does not constitute success. You can retain value with any asset you can hide, protect, and trade.
Saying a ounce of gold is always worth an ounce of gold is true but meaningless. A pound of fish is also always worth a pound of fish. Monetary utility can be assigned to any asset be it metal, paper, or digital. Gold and silver are very good forms of money but they are not perfect and they fail in the face of poor human decision making. If they didn't fail we would be using gold or silver today to purchase things.