Thread:Maddog98/@comment-4842541-20150606031801/@comment-4842541-20150621235830

Same reason how Ron Fei and his kin have the Dragon's eye. It was an ability that originated from Dragons, handed down from Dragons, and ultimately once learned can be passed down through bloodline.

In Sam's case though, it wasn't a bloodline thing. He just accidentally figured something out. Then because he has a low attention span, forgot right afterwards. Then he stole chocolate from his big brother.