Are there talismanic quotations that you know sufficiently so that you don't quite think them through? I think that's partly a result of rhythm: strict endings complete a line (that's a rule of Indo-European metrics); and rhythms structure and sometimes anchor the remembered words.
I've always loved these lines of Stevens' from "The Plain Sense of Things":
Yet the absence of the imagination had
Itself to be imagined. The great pond,
The plain sense of it, without reflections, leaves,
Mud, water like dirty glass, expressing silence
Of a sort, silence of a rat come out to see,
The great pond and its waste of the lilies, all this
Had to be imagined as an inevitable knowledge,
Required, as a necessity requires.
Some time long ago I abbreviated them, without knowing it, as "The absence of the imagination had itself to be imagined, / Required, as a necessity requires." And it was only the first of those two pseudo-lines whose meaning I thought much about. The imagination would never be absent! To think so was to rejoin it, to imagine even that. "Disillusion as the last illusion," as Stevens says in a later poem. Or Beckett's: "Imagination dead, imagine!" (my punctuation).
The end of the poem, the end of my abbreviated version, was only what filled out the stirring, saving, Berkeleyan self-contradiction of trying to imagine the imagination absent.
But now I begin to wonder why the absence of the imagination was "required"? Why makes its absence, or imagining its absence, necessary?
I think (if I thought about it at all) that I took "required" to mean just a way of repeating "had" in "had to be imagined." It is required that you do euthanize your faith. But that's because I didn't really pay attention to the "as" of the last line. As a necessity required. We need to imagine necessity too. Ananke is not the iron law we cannot escape. It is the law we imagine we suffer under, but we need to imagine it. The rat can come out to see, whenever it wants to: it's a placidly, self-contained Rilkean animal, a denizen of the immediate.
But we need necessity, and the only question is whether our need for it is enough to count as need—as we need it to be.