Buy on the Rumor, Sell on the News

I heard about this fake radar blip on the radio. I am certainly glad to hear that no one's life was in danger. But what struck me as exemplifying the bizarreness of the world we live in was that the U.S. stock and commodities markets, as well as the British and Brazilian markets, took a noticeable dip before returning to more or less their previous levels once the blip turned out to be nothing.

I wonder if the title quote to this post has an identifiable origin. The Motley Fool weighed in but they only comment on whether the adage is worth its salt and not where it came from. Searching Google shows that "fact" is a common substitution for "news" and often both instances of "on" are elided. Here is someone who agrees with the sentiment, but gets the original adage backwards.

Nothing in Bartlett's. This will mean a trip to pester my local librarian. I'll let you know how it goes.