In 1991, the World Fantasy Award for Best Short Fiction went to Neil Gaiman and Charles Vess. They won it for a stand-alone tale entitled 'A Midsummer Night's Dream'.
The prize sent shock-waves through the literary community. Fantasy genre fans and fellow authors alike were stunned. It wasn't the fact that the story wasn't fabulous (it was unbelievably good), but the medium through which it was told was the problem.
Graphic novels aren't supposed to be great. Light-weight entertainment targeting children, nerds and those without the patience to read a proper book, that was the preconceived notions of most. Yet the award had been given for a chapter in 'Sandman'.
There's an urban myth which sprang up in the aftermath, that the rules were changed to stop 'comic books' ever winning again. That's a fallacy. It's just that no other graphic novel has won before or since. 'Sandman' broke the mold.