Original subtitles

- Hi, I'm William Lidwell and this is

Universal Principles of Design.

In this movie KISS; Keep It Simple Stupid.

The acronym KISS stands for

Keep It Simple Stupid.

But more politically correct variations

are often used like Keep It Short & Simple,

Keep It Stupid Simple

and Keep It Simple Silly.

The original less politic phrasing of the

principle Keep It Simple Stupid

was popularized by Kelly Johnson the

legendary lead engineer of the Lockheed Skunkworks.

If you've never heard of Kelly Johnson

he led the design of advanced aircraft such

as the P-38 Lightening, F-104 Starfighter

and the SR-71 Blackbird.

He is considered one of the great

aircraft designers and R&D leaders

of the 20th century.

Johnson designed aircraft for war which

meant planes had to perform reliably

and they had to be easy to fix in rough,

stressful field conditions.

And one of the most powerful principles

he employed to do this was KISS.

The KISS principle asserts that simple systems

work better than complex systems.

Accordingly, simplicity should be a key goal in design.

Simplicity means minimal parts with

minimal interactions between those parts.

So given the chose between two functionally

equivalent systems, car engines, or algorithms,

or work flows, the ones with fewer parts

and interactions between parts will be

faster and cheaper to build,

will perform more reliably and will be easier

to troubleshoot and maintain.

Now, in practice it's important to note

that innovative designs rarely start off simple.

The process iteration and prototyping is messy

and designs invariably accure inessential

elements and interactions as they are developed.

The KISS principle most often comes into play

once a design nears a working prototype.

At this point KISS is a good tool to prove complexity.

Iterations become increasingly subtractive.

Good designers ask, what can be removed

without hurting performance?

And they keep removing and simplifying

and applying KISS until they can't simplify any further.

Until subtracting something hurts

a performance requirement.

That's when they know to stop.

On of the greatest examples of this type

of KISS process applied is the AK-47 Assault Rifle.

Invented by Mikhail Kalashnikov.

The AK-47 began as a kind of Frankenstein rifle.

Borrowing from a variety of existing designs.

But through this process of iterative subtraction

it was simplified to having only eight moving parts.

It is arguably the most successful firearm in history

with an estimated 70 to 100 million of the weapons

in circulation.

Tragically these very qualities have led

the rifle to become the preferred weapon of

criminals and terror its across the world.

A year before he died Kalashnikov said,

It is painful for me to see when

criminal elements of all kinds fire from my weapon.

I created this weapon primarily to safeguard our fatherland.

This serves as a healthy reminder to all designers.

The KISS principle helps give us

quality and reliability but not wisdom.

So, wether you use KISS to speed up

production processes, increase the reliability

of mechanisms, or increase the clarity and

maintainability of software remember

smart design requires that you

keep it simple, stupid.