It is not only a yardstick to measure current value, but it can measure future value. The commodity deteriorates or goes bad. The quality goes away. It is bulky and hard to transport if you need large quantities. It is hard to divide into smaller units.
People tend to keep the best quality for themselves and trade away the rest.
The poorer quality would be used for money. It tends to tie up valuable resources. Supply and Demand of a commodity are unpredictable so the amount of money is unpredictable. Gresham s Law Sir Thomas Gresham in the 16 th century developed the theory with regards to commodity money called Gresham s Law. He said bad money drives out good money.