I have acquired a new fear, thank to my fellow knitters on the internet. (Thanks, Guys.) I have been reading longer than I have been knitting, so I have had the opportunity to discover that there are levels of appreciation for reading and the books that provide such entertainment. People who take your book to Atlanta and never give it back. People who borrow your book and then give it to someone else. Or one horror I heard tell of, someone who let their child play with (not read) a book while holding a soda. (Guess how that ended.) Now, none of these people are inherently evil. They just don't treat their books the way that I treat mine. Which is fine, but it does mean I am a bit careful about who I loan books to. If it's a good book, I plan to read it again. Therefore, I want it back, in approximately the same condition it left in.
But, since you don't really lend yarn, it had not occurred to me that there were issues there. As a yarn addict, I have yarn spread throughout my apartment. (My apartment is not actually that big, but anyway.) As my yarn buying expands, I do have some precious yarn - some silk, some alpaca, or even something in a specific dye lot. It had not occurred to me - until now - to worry that people might not view my yarn with appropriate reverence. That they might toss a ball of hand-dyed silk about or put their grubby fingers on the cashmere (if I had some). So, thanks, something else to worry about.