Second principle in the red grade, Keep it simple stupid or KISS.
The KISS principle states that most systems work best if they are kept simple rather than made complex, therefore simplicity should be a key goal in design and unnecessary complexity should be avoided
Many times I have seen people overcomplicating things when it comes to software, as if complexity will make a system better. But it is just the opposite!
Complexity is the evil in software systems and ultimately a huge impediment in order to keep our code clean. We, as professional developers, have to avoid it at all cost. Keep everything as simple as possible. Build systems based in simplicity, with small classes and small methods, also avoid writing comments as much as possible - write a minimalistic code.
And don't just focus in the code when it comes to the KISS principle. Do not add features to your software that you are not going to need, do the simplest work that could possibly work, design simple to use interfaces, beware of optimisation, create the minimum documentation, and keep your processes simple following the agile/lean methodologies.
Simplistic software systems are easy to maintain, are easy to refactor and definitely easy to evolve. In this ever-changing world that we are living were markets, products, customers are changing constantly simplicity is a-must and a key to success.
As Leonardo Da Vinci once quoted and then became an Apple slogan in the 77
Simplicity is the ultimate sophistication
Also, as a personal advise do not embrace simplicity just in software, embrace it in your everyday life! :)