C.S. Lewis, Perelandra:
“What you have made me see,” answered the Lady, “is as plain as the sky, but I never saw it before. Yet it has happened every day. One goes into the forest to pick food and already the thought of one fruit rather than aother has grown up in one’s mind. Then, it may be one finds a different fruit and not the fruit one thought of. But this I had never noticed before–that the very moment of the finding there is in the mind a kind of thrusting back, or setting aside. The picture of the fruit you have not found is still, for a moment, before you. And if you wished–if it were possible to wish–you could keep it there. You could send your soul after the good you had expected, instead of turning it to the good you had good. You could refuse the real good; you could make the real fruit taste insipid by thinking of the other. […] And this is the glory and wonder you have made me see; that it is I, I myself, who turn from the good expected to the given good. Out of my own heart I do it. One can conceive of a heart which did not: which clung to the good it had first thought of and turned the good which was given it into no good.”