Simplify the following text for a Grade 6 native English-speaking person.
Original: In 1951 , Sturgeon coined what is now known as Sturgeon 's Law : `` Ninety percent of SF ( science fiction ) is crud , but then , ninety percent of everything is crud . ''
Simplified: In 1951 , Sturgeon said something that is now known as Sturgeon 's Law . He said , `` Ninety percent of SF ( science fiction ) is crud , but then , ninety percent of everything is crud . ''