As Saint Exupery said,
A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away.
And Joshua Porter adds:
Simplicity is treading a line: knowing what to keep and what to throw away. It comes across as magic when it works, because none of the complexity is transferred to users, only simplicity.
Nothing to add, really (emphasis mine)
(from Five Principles to Design By)
Great quotes, here is another favorite of mine that goes along the same lines:
“The purpose of science is to find meaningful simplicity in the midst of disorderly complexity†– Herbert Simon
I like this. Makes a good complement. Thank you, Ilya.