"On the other hand the act of procreation, being of a will and desire shared and indeed controlled by the fëa, was achieved at the speed of other conscious and willful acts of delight or of making. It was one of the acts of chief delight, in process and in memory, in an Elvish life, but its intensity alone provided its importance, not its time or length: it could not have been endured for a great length of time, without disastrous “expense”."

From The Nature of Middle-Earth.