You're not an idiot. That's an extremely cryptic riddle for a main quest, and lots of players had to look up the answer in forums.

You can't solve the riddle from that note. You are supposed to remember that there is a book with the same title that contains the whole poem, get the book, read the poem, and then answer the riddle. Of course, there is no hint that the book was so important, so if you sold the book to a shop that changed its supply, or abandoned it in a random barrel in a forgotten place, you're screwed, and cannot finish the game without help. That happened to me.

Scroll down for the answer:

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asdñlfkhjañdlsfkjñasdlfkjñlasdfkj
The answer is: "spirits"
asdlfkjñasdlfkjñasdlfkjñasldfkjdñl
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