The software engineer phrasing of simplicity is the ultimate sophistication.
Like all other principles, it is not absolute.
But it is something that you should always have on the back of your mind.
You aren't gonna need it is closely related, as generally the extra unnecessary complications are set in place to accommodate useless features that will never be needed.
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The KISS principle is an acronym that stands for "Keep It Simple, Stupid." It is a design and problem-solving philosophy that emphasizes simplicity as a key factor in effectiveness and usability. The idea behind KISS is that systems, processes, and designs should be made as simple as possible and that unnecessary complexity should be avoided.