Thanks for your input, Maybe:-), you're right about the fact texts would be more often quoted if there were a rule about it, but talking about rules, we already have 9 of these that are hardly respected, and I doubt this one would retain users" attention more than the others do.
This is why I punctually notify the requesters when they don't quote the author and the title of the poetry, song, or literary text.
About how big a text should be, let's say the sample you gave ("Io conosco la tua strada..."
wouldn't obligatorily be quoted, as it is true one can read or hear this kind of usual and short sentence elsewhere very currently, but it would become compulsory to quote A.Bocelli if the text had several lines that are belonging to the song, eg : "Io conosco la tua strada,
ogni passo che farai,... ", with some exceptions like if/when the requester is "paraphrasing" the author with a couple of lines that would match a situation s/he is actually living and reporting someone else (second degree).
But IMO, it really makes sense quoting an author when posting a text s/he wrote, this shows respect and this also helps to have instantly more context (or by using the internet search to have the integrality of the lyrics afterwards)