In practice
The usual format is: “As a [type of user], I want [something], so that [outcome].” The “so that” keeps the reason attached when the details change.
A user story isn't a specification. It is a placeholder for a conversation, with detail added through acceptance criteria.
Why it matters for product builders
Without the outcome, a story becomes a ticket. Once the reason disappears, nobody can tell whether the change still serves it.
What changes in AI-first products
The outcome matters more. A person may infer missing context from a conversation. An agent is more likely to build exactly what the story says.