Oh yeah, that once was a big problem for me when I was something like 9 years old. I was using library a lot and one day I lost the book. And there were fines for that and for late return as well. I didn't tell my parents because we didn't have a lot of money, so that would be a problem. I saved my lunch money etc for two months and then went to the library to solve the problem. They were pretty nice about it and let me to replace the book with cheap another one, which I bought right outside the library, so even didn't spend all the money I saved. Seems funny now, but it was a major source of anxiety for me back then :)