Originally Posted by WT Sharpe

Here you go, from Wikiquote:

* It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience.
o "On the Method of Theoretical Physics" The Herbert Spencer Lecture, delivered at Oxford (10 June 1933); also published in Philosophy of Science, Vol. 1, No. 2 (April 1934), pp. 163-169., p. 165. [thanks to Dr. Techie @ www.wordorigins.org and JSTOR]
o Variants: Everything should be made as simple as possible, but no simpler.
Make things as simple as possible, but not simpler.
o This may seem very similar to Occam's razor which advocates the simplest solution. However, it is normally taken to be a warning against too much simplicity. Dubbed 'Einstein's razor', it is used when an appeal to Occam's razor results in an over-simplified explanation that leads to a false conclusion. It is also similar to what has become known as the KISS Principle: Keep It Simple, Stupid! Note that the naming of the KISS principle obeys Einstein's razor, ending with a redundant letter S, which is needed to add power to the idea!

http://en.wikiquote.org/wiki/Albert_Einstein