I was just reading "A Man Young and Old" by William Butler Yeats, and when I read the following:
Like the moon her kindness is,
If kindness I may call
What has no comprehension in't,
But is the same for all
As though my sorrow were a scene
Upon a painted wall.
I was, of course, immediately reminded of the Buffy the Vampire Slayer episode "Fool For Love," and I realized for the first time that William's unrequited love for Cecily was much like Yeats's love for Maud. Oh, sure, Yeats was a better poet, and he eventually consummated his relationship with Maud, and I don't think he ever became a vampire, but otherwise the resemblance is uncanny.