After Melkor, the rebellious Vala who sought the power of Creation that he might rival Ilúvatar the Creator, destroyed Telperion and Laurelin, the Two Trees of Valinor that gave undying light to the Blessed Lands, the Valar held a council with the Eldar, to this effect:
After a time a great concourse gathered about the Ring of Doom; and the Valar sat in shadow, for it was night. But the stars of Varda now glimmered overhead, and the air was clear; for the winds of Manwë has driven away the vapours of death and rolled back the shadows of the sea. Then Yavanna arose and stood upon Ezellohar, the Green Mound, but it was bare now and black; and she laid her hands upon the Trees, but they were dead and dark, and each branch that she touched broke and fell lifeless at her feet. Then many voices were lifted in lamentation; and it seemed to those that mourned that they had drained to the dregs the cup of woe that Melkor had filled for them. But it was not so.
Yavanna spoke before the Valar, saying: “The Light of the Trees has passed away, and lives now only in the Silmarils of Fëanor. Foresighted was he! Even for those who are mightiest under Ilúvatar there is some work that they may accomplish once, and once only. The Light of the Trees I brought into being, and within Eä I can do so never again. Yet had I but a little of that light I could recall life to the Trees, ere their roots decay; and then our hurt should be healed, and the malice of Melkor be confounded.’
Then Manwë spoke and said: ‘Hearest thou, Fëanor son of Finwë, the words of Yavanna? Wilt thou grant what she would ask?’
There was long silence, but Fëanor answered no word.
Then Tulkas cried: ‘Speak, O Noldo, yea or nay! But who shall deny Yavanna? And did not the light of the Silmarils come from her work in the beginning?’
But Aulë the Maker said: ‘Be not hasty! We ask a greater thing than thou knowest. Let him have peace yet awhile.’
But Fëanor spoke then, and cried bitterly: ‘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. It may be that I can unlock my jewels, but never again shall I make their like; and if I must break them, I shall break my heart, and I shall be slain; first of all the Eldar in Aman.’
[J.R.R. Tolkien, The Silmarillion. Emphasis mine.]
Neither artist nor artisan can ever know a greater fear.