I think most people just make the mistake that it should be simple to design simple things. In reality, the effort required to design something is inversely proportional to the simplicity of the result.
-Roy Fielding
The man himself. Priceless. Goes along great with the one I did use:
A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away.
-Antoine de Saint-Exupry