Limitations of creation

[Aldarion]

I don't remember where I first read about it, but basically in Tolkien, people have a propensity to create "once in a lifetime" works that can no more be repeated, not even by their maker. Feanor and the Silmarils, Celebrimbor and the Rings of Power, Sauron and the One Ring... idea I think is that the creator puts his "heart" or "soul" into the creation.

Is there anything Tolkien wrote directly on this topic?

 

[Eljorahir]

The Two Trees are another example...

Yavanna spoke before the Valar, saying 'The Light of the Trees has passed away, and lives now only in the Silmarils of Feanor. Foresighted was he! Even for those who are mightiest under Iluvatar there is some work that they may accomplish once, and once only. The Light of the Trees I brought into being, and within Ea I can do so never again...'

--The Silmarillion, Of the Flight of the Noldor