The KISS principle states that systems work best if they are kept simple rather than made complicated.
It was used with a design perspective by an aircraft engineer Kelly Johnson, which was meant to keep simplicity as the key goal in design.
Most important goal while designing a product is to make it user friendly (take example of any app in your phone). It is quite obvious that you are using it because it is comparitively easier to use and at the same time serves the purpose.
This principle holds true whether you are designing a mobile application or a fighter plane (used in the U.S. military by Kelly Johnson).
Now, Can we implement the same thought in real life scenarios?, as not every one is planning to create a product to be used by customer. Surely, there can be many cases where keeping things simple would ultimately reduce the complications.
Psychology says that a simple personality promoting a thought can create greater impact on its audience.
Whether you are into writing or any other buisness your job is to lessen the complexity and make it easy, very easy for your audience to understand your point. The simplest solution among all is most likely to be the correct solution.
Say More With Less And Just Keep it Simple Stupid.