Why delicious and fitting to lose everything, you ask? Maybe because only in losing it can you claim you ever had it. Everything and every person is temporary and temporarily having something or knowing someone is the is the best you'll ever get. The alternative is never having it at all. Reminds me of another poem called One Art, by Elizabeth Bishop.
I can imagine Kooser lurking in the aisles of the bookstore, watching to see who is picking up his books. Of course he wants it to be a hot, sexy, yet intellectual girl who his poetry attracts. He is a MAN after all! And when she puts the book down, he makes into someone who is petty and obviously doesn't appreciat the art anyway. She's not quite as cute as she looked at first. It's about rejection. The dude got shot down!