What Is the KISS Principle?

The KISS principle is a philosophy for design and problem solving. KISS is an acronym; the letters stand for “Keep it simple, stupid.” Other permutations of the phrase have been suggested, but all have the same meaning: Complex plans or solutions can often create their own problems, so simplicity is best. The KISS principle is frequently connected with mechanical or software engineering. It can, however, be applied to most fields of human endeavor.

Many sources credit the KISS principle to American aircraft designer Kelly Johnson. Johnson, who designed planes for the U.S. military as an independent contractor, was considered unique in the engineering field for his practical approach to problem solving. His philosophy echoed the sentiments of other great thinkers of the past, including Leonardo da Vinci, Albert Einstein, and Henry David Thoreau, who famously said, “Simplify, simplify.” American president Franklin Roosevelt described a similar approach for making a speech: “Be sincere, be brief, and be seated.” The KISS principle is often quoted in modern times, when advancing technology and an expanding population have created some very complex problems.

The word “stupid” in the phrase is not intended as an insult, but rather as an admonition against the common human trait of over-analyzing or over-thinking a problem. The KISS principle is related to another common problem-solving approach, in which a large, complex problem is broken down into its smaller components, which can then be solved individually. This is sometimes called the divide-and-conquer approach. In science, a related concept is Occam’s razor, or the law of parsimony. Occam’s razor recommends that a theory or hypothesis be kept as simple as possible by excluding all factors except those that have a proven relationship to the matter at hand.

The acronym in the KISS principle has been given other meanings than “Keep it simple, stupid.” These include “Keep it simple and straightforward,” “Keep it short and simple,” and “Keep it stupid simple.” The latter phrase, while not grammatically correct, reminds designers that their creations will be maintained by others who do not have the same amount of time, money, or intellect. Kelly Johnson echoed this philosophy, reminding engineers that military aircraft must be simple enough to be repaired in the field. These crucial repairs are often made by mechanics with limited tools and time, sometimes under combat conditions.

A variation on the KISS principle is the saying “It’s the economy, stupid.” This phrase was coined by political adviser James Carville during the 1992 U.S. presidential campaign. It was quickly adopted as a slogan by candidate Bill Clinton, suggesting that many of America’s far-reaching problems had their roots in economic matters. It became a popular catchphrase and is credited with helping Clinton win the presidency. Since that time, many political discussions and campaigns in the U.S. have employed some variation of the phrase “It’s the economy, stupid.”