Which is not a feature of a user story?

A user story is a brief, simple explanation of a feature told from the perspective of the end user. It captures what the user needs and the value of that need. Key characteristics of a well-structured user story include being negotiable, which emphasizes flexibility and adaptability in defining the requirements; testable, ensuring that the story can be validated against acceptance criteria; and estimable, allowing teams to make educated guesses on the effort required to implement the story.

While "achievable" might seem relevant, it is not traditionally listed among the core characteristics of a user story. User stories should focus on the output being aligned with user needs and the value they bring, rather than explicitly stating that the goal is achievable. Achievability can often be inferred through negotiation and estimates, but it is not explicitly defined as a feature of a user story itself.