Years ago I was introduced to the K.I.S.S. theory. “Keep It Simple Stupid”. It’s a world class theory. Maybe the most important thing I ever learned. To me it’s less theory and more mantra.
According to Wikipedia, “theory” is: “a contemplative and rational type of abstract or generalizing thinking”.
The same source refers to mantra as: “a sacred utterance, sound, or a syllable, word, or group of words believed by some to have psychological and spiritual power”. Now that’s what I’m talking about!
Personally, I never, ever, repeat to myself or in my mind or over and over in my head for effect, guidance or as reminder – a theory. Ask yourself, when trying to stay focused, do you every say to yourself” E=mc2, E=mc2, E=mc2? Ever?
On nearly a daily basis my subconscious tries to remind me to “keep it simple stupid”. Sometimes I listen. Sometimes not. I can be stupid. But I strive to be 
simple. My results are always better when I keep it simple. People confuse activity for accomplishment. Mistake complexity for sophistication. Leonardo da Vinci said, “simplicity is the ultimate sophistication”.
I’ve decided, simple is the ultimate art form. Go to a paint store, ask for white paint. You will not be shown 40 shades of grey, but 40 different shades of white! I usually walk out.
Chaos is born in complexity. Need an example, look at the U.S. Tax Code. Simplicity is the product of a clear mind and confidence. Keep it simple or risk being stupid.
An old race horse trainer once told me, “Training horses is simple. Keep’em fat and happy and breeze’em a half a mile. They’ll win in spite of you.” He’s in the Hall of Fame.