When I read a sample for a writer of sci-fi and/or fantasy I am unfamiliar with, I decide if I will try the book based on a simple feeling . . . can I buy the premise?
Perhaps it should be called PRE - MISS . . . if the writer misses me now, I doubt I'll look at other works later.
A writer's imagination fuels their story, but their imagination alone cannot create an experience for me as a reader. I need my imagination engaged. To do this I have to "believe" in the fantasy.
The book description helps. The first couple of chapters, often the SAMPLE made available, must complete the process.