What impresses one about these vast achievements of genius is that the gift involves knowing how much work is necessary, and then knowing when to stop. We will never know what books or musical compositions, theorems, sketches and models were laboured over and then discarded, although it is certain, I think, that the genius's willingness to expend a great deal of effort is usually tied both to an uncanny gift for seeming to judge in advance how much effort is needed, and knowing also when no more is needed. It's as if a prior shape for the work exists in the creator's mind, and that can only be realised by labour-intensive work that allows no shortcuts or quick fixes. Rodin's statue the Burghers of Calais seems to be there in all of its early versions, requiring only that final bit of polish before its ultimate clarity is achieved. Genius may require plodding, but the work isn't at all like that of Sisyphus, rolling the rock uphill only to have it fall back down before the summit is reached.
Genius is productive.
What is specially moving about Marcel Proust is his withdrawal from the world in order to complete his great novel, to live in isolation and silence, and even while literally taking his last breath to be correcting, adding to, and crossing out words in his publisher's proofs. Only death seems to have stopped his prodigious labours. Rather than thinking of genius as the triumph of divine will power over fate and average gifts, we would be more accurate in seeing it poignantly as an everlasting effort to get the work right, always leaving room for the nagging doubt that it never was right, never actually made it, didn't in the end succeed. This is as true of a modern restless genius like Bertrand Russell, philosopher, mathematician, visionary, peripatetic rebel, as it was of Beethoven. The products of genius are precarious, by no means guaranteed in their outcome, and, alas, derive from often thankless effort.