In reality, whether a donor comes back for another year is entirely in your hands. And no, the work doesn’t happen during the initial ask letter or the renewal appeal. It happens for the entire duration of the year in between.
When a donor is deciding whether or not to renew, they’re not paying attention to what you wrote in their renewal letter, they’re thinking about the past year of their membership. Did they have a good experience? Did they get value out of being a member of your community? Do they feel an emotional tie to the organization? Do they feel that their contributions made a difference in your ability to create positive change?