The trick to finding forgotten books for people

is to keep a small list of frequent flyers in your head. If the details can be cut or stretched to fit one of the 50 - 100 most commonly requested books, then that's probably it. (Sometimes you even guess one right where every detail was wrong.)

The trouble with this method is that if you have a forgotten book, odds are nobody else has ever heard of it, because it's not one of the top 100 books, or even the top 500.

This is very annoying, but I keep asking anyway.

(What's really annoying is when you know you asked before and got an answer, but now you've forgotten again.)