In "build a booking feature", the AI doesn't know who's booking, what they're booking, or what happens after. A user story forces you to say all three:

As a (who), I want (to do what), so that (I get what).

作为 到店顾客，
我要 在手机上选一个时间段提交预约，
为了 不用打电话也能确定我那天有位子。

作为 店员，
我要 在后台看到今天所有预约并标记「已到店」，
为了 不用再翻微信聊天记录核对。