There's no doubt about it—when the first poem in your first book of poems announces that you burn brightly and quickly, it's pretty easy to see that you think you're the cat's meow. And while Millay suffered from many things, lack of ego was not one of them. "First Fig" proclaims the artist's brilliance and the woman's provocativeness in no uncertain terms. Luckily, it's cheeky enough to also be entertaining. Forget endearing—that's for simpler, less exciting poets to worry about. Millay wants to dazzle.
The speaker's acknowledgement that her light won't last long makes it seem like she's humble about her brilliance. Aw, shucks.
This poem works as a metaphor for literary production: even the brightest of literary stars tends to fall out of fashion very quickly. Sad.