Keep It Simple Stupid variations: Keep it short and simple / Keep it smart and simple / Keep it simple, silly.
Most systems work best if they are simple. A simple design should be the key goal. There is a direct correlation between the simplicity of an explanation or a product and its usefulness, meaning simpler is more useful. KISS is not meant to imply stupidity.
On the other hand, the focus must be kept on achieving the goal. Oversimplification is dangerous if the goal cannot be achieved because of it.
The KISS principle can be used almost everywhere, including programming, public speaking, design, etc.
“Make everything as simple as possible but not simpler” – Albert Einstein
“Simplicity is the ultimate sophistication” – Leonardo Da Vinci