How I did it: I had prepared two notes previously, both of which magically disappeared everytime I tried heading out to the library. Again today, as I showed up in the books stacks, i realized the note I'd written wasn't, in fact, with me. I decided that I wouldn't let fate mess with me any longer, borrowed a scrap of paper and a pen from the desk clerks and quickly scribbled a note about unrequited loved. I snuck it into one of the very rare English-language books in this supposedly bilingual library, and rushed out.
Lessons & tips: Don't overthink the letter. Think of someone you know, and write that note for them. The more specific you will be, the more enticing and mysterious the message will be for the person who might potentially discover it some day. Remember, you will, in all probability, be present if and when the letter should be discovered, nor will you ever learned how the discoverer reacted. Suffice it to say that the romance in this act comes from the idea that you went through with it at all, and the possibilities that emerge from it, rather than the facts themselves.