He entered the cave and yelled Fafnir's name, to which he quickly appeared. Siegfried made quick work of the dragon, and in so doing caught a bit of the beast's blood on him. This allowed him to hear the language of the birds who spoke of him and his quest. This was how he learned of the dwarf's plan to betray him for the treasure, and that he would become invincible if he bathed in the dragon's blood. I'm reminded of Achilles dipped in the River Styx with his only his heel exposed, down to the leaf which fell on Siegfried's shoulder covering his future weak point. He then goes on to many adventures throughout his life before being killed by his wife in an argument. You could make the comparison to King David, who brought down Goliath and became a ruler, but not without scars on his moral track record to follow his great victory.
 
Though ever I search, when will I find
Final reconciliation of body and mind
Try as I might, paranoia running blind
Training to hold my tongue to divine
The answer to apparitions invented by design
Coming through the aperture of endless insights
Sword turned against demons, legions to fight
The wisest turn their faces toward the light
 
Created by Denver Artist Matt Maes - Surreal Mythical Art