[Maédhros]

From the Published Silmarillion

But as the theme progressed, it came into the heart of Melkor to interweave matters of his own imagining that were not in accord with the theme of Ilúvatar, for he sought therein to increase the power and glory of the part assigned to himself. To Melkor among the Ainur had been given the greatest gifts of power and knowledge, and he had a share in all the gifts of his brethren. He had gone often alone into the void places seeking the Imperishable Flame; for desire grew hot within him to bring into Being things of his own, and it seemed to him that Ilúvatar took no thought for the Void, and he was impatient of its emptiness. Yet he found not the Fire, for it is with Ilúvatar. But being alone he had begun to conceive thoughts of his own unlike those of his brethren.

This has always interested me. Why would only Melkor feel this way among the Ainur? Why does he has that innate curiosity that the others lack?
From Morgoth's Ring: Myths Transformed

Melkor must be made far more powerful in original nature (cf. 'Finrod and Andreth'). The greatest power under Eru (sc. the greatest created power). (He was to make/ devise / begin; Manwë (a little less great) was to improve, carry out, complete.)
Melkor 'incarnated' himself (as Morgoth) permanently. He did this so as to control the hroa, the 'flesh' or physical matter of Arda. He attempted to identify himself with it. A vaster and more perilous, procedure, though of similar sort to the operations of Sauron with the Rings. Thus, outside the Blessed Realm, all 'matter' was likely to have a 'Melkor ingredient', and those who had bodies, nourished by the hroa of Arda, had as it were a tendency, small or great, towards Melkor: they were none of them wholly free of him in their incarnate form, and their bodies had an effect upon their spirits.

I had always thought that Melkor strayed from his path. To me at first, he was the one to have become like the great architect of the making of Arda, while the other Valars put their touches here and there. But now I think that perhaps I was mistaken.
Perhaps a world like that was to be flawed, perhaps it was that the reason that Melkor had such other ideas unlike his brethren.
What if Melkor's devise to make begin, was not meant for Arda but for Arda Remade? Consider, Melkor "incarnated" his power to the flesh of Arda, leaving no choice but to make it anew. With all of his interference he enriched the overall history of the world and that of Men, so that they should be an integral part of the remaking of Arda. By having struggles in Arda, wouldn't that make in the end the joy of victory that much sweeter?
If the only part of Arda was Valinórë, which had no Melkor ingredient on it, and yet Men could not live there and it was a constant source of grief in Men, would that not be wrong. Perhaps that is what Melkor saw and that is what led him to his ways. Perhaps Arda Remade was the way that all of the beings could live in perfect harmony together and Melkor was the one who began it all.