A Dragon's Hoard
It's widely known that dragons are giant creatures that fly around burning castles and plundering treasures, which they gather together into a hoard beneath their lair.
It's less widely known why exactly dragons do this. Many creatures hoard food, or nest-building materials, but the treasure kept by a dragon is neither. So why this behavior?
Well, it goes back to the origin of dragons. In the elder days, after the gods cursed mortalkind with death, everything was in disarray and everyone was terrified of their mortality, wizards especially. And, being wizards, they devised a means to strike back at the gods.
In those days it was true that, despite mortal spellcraft, no god could be touched or seen by a living being unless it wished to be. Therefore, wizards had no way to harm the gods in vengeance.
This is where dragons come into the story. Mortal wizards - not the gods - made these dangerous creatures. In the beginning, they were meant to lead bands of heroes on attacks into divine domains, much like a troop assault ship 'leads' a group of marines into an amphibious invasion.
But these heroes would need mighty magic weapons to contend with the gods and their hosts. So dragons were ingrained with a compulsion to gather magical artifacts from their surroundings, and gather them into a repository the heroes could easily find.
Obviously, the gods were having none of that, and after all the wizards involved in the creation of dragons were shot into the sun, the god Razghol, who had already brought the curse of death, brought a second great curse to mortalkind. For their impudence, dragons would forever devastate their lands, burn their castles, and steal their treasures.
Sadly, Razghol has no finesse, and he never thought to have dragons, say, destroy the magic weapons once captured...