Why does the masque suddenly disappear when Prospero remembers the plot against him by Caliban and his crew? What is Shakespeare suggesting by contrasting these two events?

Prospero calls upon Iris, the messenger of the gods and also the goddess of the rainbow, to perform a betrothal masque for Ferdinand and Miranda. The masque, which he created from his own power, disappears in an instant; and finally, Prospero realizes that his works of magic are all in vain, as they are made of "baseless fabric" and will not last. He sees that "we are such stuff as dreams are made on," and at last realizes that his mind has aged and his powers are fragile and faltering (IV.i.166-167). It is a sobering moment for Prospero, to admit his "weakness" and "infirmity"; and this marks the beginning of his surrender of his magic.