The proper posture for the creature is one of receptivity. In Perelandra we see several ways in which this posture could be corrupted or destroyed. First it is always possible to seek ways to assure ourselves of repeating the pleasure. This is what makes money so suspect in Lewis' eyes - it is a means by which we assure ourselves that we can have the pleasure whenever we want it. It provides a measure of independence. One no longer has to throw oneself into the wave. Second, even when one pleasure is given, it is (as the Lady discovered) possible to turn from what is given to something which is (thought to be) preferred. And this, in turn, is what makes a life oriented toward the future suspect for Lewis - to commit too much of one's hopes and happiness to the future will make impossible the posture of receptivity appropriate to a creature.
In either case-whether we try to secure means for repeating the pleasure at will or turn from what is given to something else which is desired - Lewis thinks that we will eventually lose the capacity for delighting in what is received. For to treat a created thing as something more than that is to destroy its true character. To seek in any created thing a complete fulfillment of the longing which moves us is to make of it an object of infinite desire and, because it is only a created thing, a false infinite. It may still be sweet, at least for a time, because it is intended by its Giver to be a source of delight. But in the end it will be poison for the person who gives his heart only to it. Hence the constant temptation: the lure of the sweet poison of the false infinite.
Source: The Taste for the Other: The Social and Ethical Thought of C. S. Lewis, Pages: 18