That's funny, I often think of a similar maxim in the book "Groucho and Me" by Groucho Marx. Essentially, he said that in 1928-29, he knew it was time to get out of a certain stock once his taxi driver started talking about it.

It's a great book, you can find most of the text here : http://books.google.com/books?id=tFsnGr2SQJ0C&printsec=f... though I can't find the section about the cab driver. The whole part about the 1929 stock crash is great.