KISS, an acronym for "Keep it simple, stupid!", is a design principle noted by the U.S. Navy in 1960. First seen partly in American English by at least 1938, the KISS principle states that most systems work best if they are kept simple rather than made complicated; therefore, simplicity should be a key goal in design, and unnecessary complexity should be avoided. The phrase has been associated with aircraft engineer Kelly Johnson. The term "KISS principle" was in popular use by 1970. Variations on the phrase (usually as some euphemism for the more churlish "stupid") include "keep it super simple", "keep it simple, silly", "keep it short and simple", "keep it short and sweet", "keep it simple and straightforward", "keep it small and simple", "keep it simple, soldier", "keep it simple, sailor", "keep it simple, sweetie", or "keep it sweet and simple".
The acronym was reportedly coined by Kelly Johnson, lead engineer at the Lockheed Skunk Works (creators of the Lockheed U-2 and SR-71 Blackbird spy planes, among many others). However, the variant "Keep it Short and Simple" is attested from a 1938 issue of the Minneapolis Star.
While popular usage has transcribed it for decades as "Keep it simple, stupid", Johnson transcribed it simply as "Keep it simple stupid" (no comma), and this reading is still used by many authors.
The principle is best exemplified by the story of Johnson handing a team of design engineers a handful of tools, with the challenge that the jet aircraft they were designing must be repairable by an average mechanic in the field under combat conditions with only these tools. Hence, the "stupid" refers to the relationship between the way things break and the sophistication available to repair them.
The acronym has been used by many in the U.S. military, especially the U.S. Navy and United States Air Force, and in the field of software development.
The principle most likely finds its origins in similar minimalist concepts, such as:
Heath Robinson machines and Rube Goldberg's machines, intentionally overly-complex solutions to simple tasks or problems, are humorous examples of "non-KISS" solutions.
Master animator Richard Williams explains the KISS principle in his book The Animator's Survival Kit, and Disney's Nine Old Men write about it in Disney Animation: The Illusion of Life, a considerable work of the genre. The problem faced is that inexperienced animators may "over-animate" in their works, that is, a character may move too much and do too much. Williams urges animators to "KISS".
Remember the adage KISS; Keep it Simple, Soldier