"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away" -- Antoine de Saint-Exupery (1900 - 1944), a French writer.
Complexity is confusing. Simplicity is soothing.
Some illustrative examples: Google homepage and aphorisms, sayings, quotations, and short concise guidelines in books like the Bhagwad Gita. Mathematicians and scientists strive to simplify theories to few basic principles and ideas. Good composition of photographs requires removal of extraneous elements from the picture frame while retaining its essence. Class design in object oriented languages calls for minimalist interfaces. Keep it simple, stupid! is a recurring theme in computer systems design. In a memorable sequence of ink-removal steps, Edward Tufte beautifies a graph in his classic book Visual Display of Quantitative Information. This book is recommended reading for anybody who ever draws a graph in a research paper or a presentation.
A memorable quote from Radia Perlman's interview in March 2014:
“My designs were so deceptively simple that it was easy for people to assume I just had easy problems, whereas others, who made super-complicated designs (that were technically unsound and never worked) and were able to talk about them in ways that nobody understood, were considered geniuses.”