Tolkien focuses on the potential dangers of conflict between oath and family loyalties when he describes the Kinslaying of the Teleri; the legends of the Tuatha De Danaan show how the oath can be used to defend or avenge wronged kinsmen, as when Lugh avenges his father.
The cultures of the Tuatha De Danaan and Noldor are destined to end in another, less dramatic fashion that involves neither destruction nor death--only a very soft, slow fading away.
The contrast is stark between the transcendent Tuatha De Danaan and the corporeal Milesians, called the "eponymous ancestors of the modern, mortal Irish" by Gerald Gillespie (8).
Following this relocation in accordance with the "agreement of the Tuatha De Danaan to dwell underground, in ancient barrows and cairns" as well as other isolated places in the world, the motif of the hidden house emerges (Fimi 163).
When Scathniamh finally comes to him towards the end of his life, Caoilte explains to onlookers why such a beautiful young girl is with such an old man: "I am of the sons of Miled that wither and fade away, but she is of the Tuatha De Danaan that never change and that never die" (80).
The legend of Scathniamh and Caoilte is barely a footnote to the story of her father, Bodb Dearg, who plays a much more prominent role in Tuatha De Danaan legend and politics when a struggle of, literally, godlike proportions breaks out between the Dagda's sons over who will assume kingship on their father's death.
Because it is not enough that the Tuatha De Danaan and Noldor fade into the natural world; the dominion of men necessitates that they leave the world altogether.
Despite these supernatural qualities, the Otherworlds of the Noldor and the Tuatha De Danaan are not inaccessible; in fact, they can be reached by concrete methods.