'work they may accomplish once, and once only' -- Silmarillion, p. 78

In a single chapter of The Silmarillion we learn that some creative acts require so much of their makers that they can perform them only once. 

Yavanna says she cannot repeat the creation of the Two Trees -- 'Even for those who are mightiest under Ilúvatar there is some work they may accomplish once, and once only' --  but that she could use the light of the Trees locked within the silmarils to revive them, if only Fëanor would break them (78).

Fëanor replies that  'for the less even as for the greater there is some deed that he may accomplish but once only; and in that deed his heart shall rest' (78). His creation of the silmarils is of the same order as hers of the Trees, and, 'if I must break them, I shall break my heart, and I shall be slain' (78).

When Fëanor demands that the Teleri give up their ships so that the Noldor can pursue Morgoth to Middle-earth, the Teleri respond that '[our] ships are to us as are the gems of the Noldor: the work of our hearts, whose like we shall never make again' (86).

Today I was discussing these passages with my friend, Richard Rohlin, of the Amon-Sûl podcast at www.ancientfaith.com. As we were talking it occurred to me that, while it might seem odd to think of Sauron as having a heart, especially one that ever rests, he did put so much of his power into making the One Ring that its destruction was virtually his own. So there is a certain analogy here.