Suppose that you are a big fan of the Harry Potter books. You would love to own a copy of the very first printing of the first book, but unfortunately you can't find it for sale for less than $5,000. You are willing to pay at most $200 for a copy but can't find one at that price until one day in a used bookstore you see a copy selling for $10, which you immediately buy. Are you being irrational if you keep the copy rather than sell it?