What is the dominant effect of irony?

In his chapter 26 Foster describes the prevailing and even dominating effect of literary irony. If a text is written in an ironic mode, than any symbolism, associations, or traditional uses of meaning go out the window. If the text explicitly discusses a journey or quest, for instance, a literary convention that suggests growth, self-knowledge etc., but at the same time makes use of irony, then one should expect the "quest" to meaning anything but that. The "ironic mode," first formally identified by literary theorist Northrop Frye, refers to a text in which the characters possess lesser autonomy, self-determination or free will than ourselves, which means we know something they don't quite realize themselves. As readers, we also can see consequences that elude the characters in the text. In T.S. Eliot's "The Wasteland," the onset of spring ("April is the cruellest month") does nothing to revive or rejuvenate the wasteland described.