The story of how "Unicorn Variation" came to be written. As The Other Wiki puts it:
"Unicorn Variation", was written as a result of Zelazny having been asked to contribute to two different upcoming anthologies — one collecting stories set in bars, and one collecting stories about unicorns. When Zelazny mentioned these requests to his close friend George R. R. Martin, the other told Zelazny of a third upcoming anthology — one which would collect stories about chess — and jokingly suggested that Zelazny write a story about playing chess against a unicorn in a bar, so that he could sell the story three times. Zelazny did just that and then went on to win a Hugo Award for the story.
The comments by the editors of the bar stories anthology (Tales From The Space Port Bar) make it quite clear that even without the obvious quality of the story in question, they would have bought it anyway just because they were so impressed by Zelazny's chutzpah.