From Proust's "In Search of Lost Time", second part:
"Now the memories of love are no exception to the general laws of memory, which in turn are governed by the still more general laws of Habit. And as Habit weakens everything, what best reminds us of a person is precisely what we had forgotten (because it was of no importance, and we therefore left it in full possession of its strength). That is why the better part of our memories exists outside us, in a blatter of rain, in the smell of an unaired room or of the first crackling brushwood fire in a cold grate: wherever, in short, we happen upon what our mind, having no use for it, had rejected, the last treasure that the past has in store, the richest, that which, when all our flow of tears seems to have dried at the source, can make us weep again. Outside us? Within us, rather, but hidden from our eyes in an oblivion more or less prolonged. It is thanks to this oblivion alone that we can from time to time recover the person that we were, place ourselves in relation to things as he was placed, suffer anew because we are no longer ourselves but he, and because he loved what now leaves us indifferent. In the broad daylight of our habitual memory the images of the past turn gradually pale and fade out of sight, nothing remains of them, we shall never recapture it. Or rather we should never recapture it had not a few words been carefully locked away in oblivion."
A similarly beautiful passage occurs in the first part:
"But when from a long-distant past nothing subsists, after the people are dead, after the things are broken and scattered, still, alone, more fragile, but with more vitality, more unsubstantial, more persistent, more faithful, the smell and taste of things remain poised a long time, like souls, ready to remind us, waiting and hoping for their moment, amid the ruins of all the rest; and bear unfaltering, in the tiny and almost impalpable drop of their essence, the vast structure of recollection."