The quest for the origin of the saying known as ‘Hanlon’s Razor’ continues! I recorded Joe Biglen’s correspondence here and here last year, where he describes how Robert J. Hanlon, a friend of his, contributed it to a book published in 1980.
Today, Scott Enderle writes that it may be a variation on a sentence in Robert Heinlein’s “Logic of Empire” (1941):
“You have attributed conditions to villainy that simply result from stupidity”
So it may have been Heinlein’s Razor before Hanlon’s. That two Roberts with similar surnames should both be credited with the same phrase seems remarkable. Perhaps Heinlein was the originator, but Hanlon also deserves some credit for publicising it in the form which became widely known.