Hanlon's razor

Hanlon's razor is an adage or rule of thumb that states:
 * Never attribute to malice that which is adequately explained by stupidity.

It is a philosophical razor that suggests a way of eliminating unlikely explanations for human behavior. It is probably named after Robert J. Hanlon, who submitted the statement to Murphy's Law Book Two (1980). Similar statements have been recorded since at least the 18th century.

Origin
The adage was a submission credited in print to Robert J. Hanlon of Scranton, Pennsylvania, in a compilation of various jokes related to Murphy's law published in Arthur Bloch's Murphy's Law Book Two: More Reasons Why Things Go Wrong! (1980).

A similar quotation appears in Robert A. Heinlein's novella Logic of Empire (1941). The character Doc in the story describes the "devil theory" fallacy, explaining, "You have attributed conditions to villainy that simply result from stupidity."

Hanlon's razor became well known after its inclusion in the Jargon File, a glossary of computer programmer slang, in 1990. Later that year, the Jargon File editors noted lack of knowledge of the term's derivation and the existence of a similar epigram by William James, although this was possibly intended as a reference to William James Laidlay. In 1996, the Jargon File entry on Hanlon's Razor noted the existence of the phrase in Heinlein's novella, with speculation that Hanlon's Razor might be a corruption of "Heinlein's Razor". The link to Murphy's law was described in a pair of 2001 blog entries by Quentin Stafford-Fraser, citing emails from Joseph E. Bigler. In 2002, the Jargon File entry noted the same. The Jargon File now calls it a "Murphyism".

The name was inspired by Occam's razor.

Other variations of the idea
A variation appears in The Wheels of Chance (1896) by H.G. Wells:"There is very little deliberate wickedness in the world. The stupidity of our selfishness gives much the same results indeed, but in the ethical laboratory it shows a different nature."A similar quote is also misattributed to Napoleon. Andrew Roberts, in his biography of Winston Churchill, quotes from Churchill's correspondence with King George VI in February 1943 regarding disagreements with Charles De Gaulle: His 'insolence ... may be founded on stupidity rather than malice.

Douglas W. Hubbard quoted Hanlon's razor and added "a clumsier but more accurate corollary ...: 'Never attribute to malice or stupidity that which can be explained by moderately rational individuals following incentives in a complex system.'"