Sturgeon's Law

It is in this vein that I repeat Sturgeon’s Revelation, which was wrung out of me after twenty years of wearying defense of science fiction against the attacks of people who used the worst examples of the field for ammunition, and whose conclusion was that ninety percent of it is crud.

The Revelation
Ninety percent of everything is crud.
Corollary 1
The existence of immense quantities of trash in science fiction is admitted and it is regrettable; but it is no more unnatural than the existence of trash anywhere.
Corollary 2
The best science fiction is as good as the best fiction in any field.

Venture Science Fiction magazine