Whatever flames upon the night
Man’s own resinous heart has fed.

In these lines Yeats imagines the night lit not by an external, benevolent fire but by a blaze fueled from within: “man’s own resinous heart.” Resin suggests something sticky, combustible, and drawn from a wounded tree—an image that links human passion to both injury and ignition. The thought implies that what flares in the darkness—desire, violence, visionary intensity, or destructive fervor—is often self-generated and self-sustaining. The couplet compresses a bleak moral psychology: the brightest flames may be fed by inner substances that are volatile and hard to purge, so the night’s illumination is inseparable from the heart’s capacity to burn.