My sister said something about writing prompts that actually made me stop and think

We were talking about a prompt I liked, 'a locked door that only opens at midnight,' and she just shrugged and said, 'That's just a thing, not a story. Who's trying to open it and why are they desperate?' It hit different because I realized I'd been collecting cool 'things' instead of figuring out the human stakes behind them. How do you turn a neat image into a character someone cares about?