Back in 1967, I was sitting in my living room in Sea Cliff, Long Island, wondering what sort of creatures I could use in my next story. Since S-F is a “what-if” form of fiction, I suddenly wondered, “what if dragons were the good guys?” Then I had to develop a planet which needed a renewable airforce against some unknown menace and came up with Pern, dragons, Thread and humans who Impressed a hatchling in a lifelong symbiotic relationship. Rather wonderful to have an intelligent partner that loves you unconditionally. Who wouldn’t like a forty-foot telepathic dragon as their best friend? By the time my (then) children got home from school, I knew how it would all start: “Lessa woke cold.” I finished Weyr Search by summer and John W. Campbell bought it immediately for ANALOG Magazine and asked me to do more stories about Pern.
Guess that answers that. Pern started out as an idea series, not milieu.