Sometimes while reading news or watching a movie or by something else I remember about some book I read. Sometimes it's just the particular instance in the book or I remember the full story but I cannot remember the name of the book. For example, you read about Plagiarism and you remember about the book where somebody killed somebody else because of Plagiarism. You remember this bit, but cannot place the book. You wonder what book it is. X is for the unknown book.
Has this happened to you? Have you wondered where I have read this before?