Keep It Simple, Stupid (KISS)

Allegedly coined by aircraft engineer Kelly Johnson, the KISS principle makes simplicity a key goal in design by stating that most systems work best if they are kept simple.

One day, Kelly Johnson handed his 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, only using these tools—forcing them to keep the design stupidly simple.