Never played UO, but I saw this material given as a talk at GDC.
When they set their designs on a closed-loop material economy, they didn't account for extravagant hoarding behavior such as building houses from stacks of leather boots. Occasionally, they couldn't spawn new monsters because the world had ran out of the raw materials the monsters were supposed to drop as loot! They had to inflate the economy several times while trying to find yet another policy fix.
When they set their designs on a closed-loop material economy, they didn't account for extravagant hoarding behavior such as building houses from stacks of leather boots. Occasionally, they couldn't spawn new monsters because the world had ran out of the raw materials the monsters were supposed to drop as loot! They had to inflate the economy several times while trying to find yet another policy fix.