"...the unknown reader I sometimes say I imagine..."
In The Believer Book of Writers Talking to Writers, James Salter (talking with Dan Pope) brushes past a question about formal recognition of an author's accomplishments (publication, awards, etc.) and reflects on a surprise reader reaction to one of his books:
There are few thrills like the first one, but not long ago at a party a woman I was being introduced to said simply, "Did she really just read a magazine?" She was referring to a scene in A Sport and a Pastime. She assumed I would know. My God, all the things of inconsequence she might have said! I don't remember her name, but she was the unknown reader I sometimes say I imagine, the woman in her thirties or forties who perhaps lives in Buenos Aires.
It must be a thrill for any writer to encounter a reader who mentally retains the big themes or major characters or settings of one of the writer's books, but even more so when they remember a tiny detail like the one Salter mentions. That shows how vividly rendered the tiny detail was, which really points out the writer's skill. Most writers can nail the big theme or major character, but if one can also nail the tiny details, now that's a real writer.
I also like Salter's idea of the "unknown reader", which to me means that one reader out there which the writer is trying to connect with. It might mean simple motivation for the writer ("This is who I'm writing the story for") or a reality check. For me it's the latter. When I'm writing, now and then I imagine a few specific (not "unknown") family members and friends as future readers, and ask myself: "Would my reader think this character is believable? That this is really how people talk? That this plotline is plausible?" All of which keeps me grounded.