The wanderlust governs the world of an adventurer.
It's the reason that every would-be fighter picks up a sword and its why a thief needs to steal and its why you keep going when the torch goes out and you hear something stir in the deep.
It's also what creates dragons.
Because dragons aren't just the reason you risk your life in the catacombs that snake beneath the earth. They are what you become when the journey isn't enough any more, when a damp cave floor feels better than a warm bed, and a gold coin looks good enough to eat. Why?
Maybe it was the hired hands you sacrificed, with promise of gold and glory you lured them to delve. They were young and stupid and when the color faded from their flushed and blotchy cheeks you could still see the lust in their eyes. They knew what this was and they lived like explosions. Swords drawn they screamed their lovers names and ran. They meant nothing to you, they died locked in combat with beasts that drank water from black pools. Things that would live a hundred years and never breath fresh air.
Maybe it was the friends you betrayed. The hand you let slip so as to grab the rough of a burlap sack so full of a life of luxury it makes your mouth water now just to think about it. And luxury you have, seated on the golden thrones of a murder of kings. You will feed on it, first in your mind and then with your mouth. And then the fire starts, deep in your guts it begins to itch and to smoke and you fill your furnace with gold until it runs down your newly scaled face like soup. One hundred years goes by and you are still hungry.
You roam the countryside, searching for kingdoms to devour, you eat your fill. Lust turns to greed.
One thousand years and you are a starving king, feasting and spewing molten gold onto your soon to be loyal subjects. They die in a river of your fire and are reborn in your visage. Snake and stone, draped in the finest furs and grinning with the same obsidian teeth. They look upon you as a god, for you hold their salvation in your furnace. Only death by your hand will free them from hell.
You will be the subject of songs and stories and the nightmares of a thousand children. You will be hunted. Some fool will get lucky and your head will stare down from the spire of a keep in some far off kingdom. Wars will be fought over your hoard, and more will be financed by it. Your coins will fill the pockets of kings, sellswords and pirates, and be stolen from them by a child now grown. A child who stared up at your lifeless eyes and felt the same thing that you felt ten thousand years ago.