How many user stories does it roughly take before a product owner has a basic fluency in writing user stories? Meaning that the idea of writing user stories has moved beyond theory, rough execution, and the product owner naturally knows what to do when writing user stories.
Just to be clear, I'm not just asking how long it takes, but how many real stories it takes. Meaning to me, saying how long is not as meaningful as how many stories, though that might be flawed, and if so, then I guess the best answer would explain why, and what would be the best measure.
Also, my assumption is that the product owner would be engaging a team that already knows what they're doing.