Sturgeon's revelation, commonly referred to as Sturgeon's law, is an adage commonly cited as "ninety percent of everything is crap." It is derived from quotations by Theodore Sturgeon, an American science fiction author: while Sturgeon coined another adage that he termed "Sturgeon's law", it is his "revelation" that is usually referred to by that term.

The phrase was derived from Sturgeon's observation that while science fiction was often derided for its low quality by critics, it could be noted that the majority of examples of works in other fields could equally be seen to be of low quality and that science fiction was thus no different in that regard to other art.

http://en.wikipedia.org/wiki/Sturgeon%27s_Law