There is more to User Stories than filling out a form. The "as a <user>, I want <something> so that I can <some benefit>" template is intentionally inadequate to capture details. Why is that? The general answer is that the details emerge from a conversation with the actual user. You may have heard the statement that User Stories are not about documentation; they are about conversation. This is true, but the conversation is more than just a further elicitation of detail. User Stories are about possibilities!