From C.S. Lewis' Perelandra:
"...it may be, one finds a different fruit and not the fruit one thought of. One joy was expected and another is given. 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 got. You could refuse the real good; you could make the real fruit taste insipid by thinking of the other."
"And have you no fear... that it will ever be hard to turn your heart from the thing you wanted to the thing Maleldil sends?"
"...The wave you plunge into may be very swift and great. You may need all your force to swim into it. You mean, he might send me a good like that?"
"Yes--or like a wave so swift and great that all your force was too little."
"It often happens that way in swimming," said the Lady. "Is not that part of the delight?"