I used to get stuck trying to write a whole story from a prompt

For years, I'd see a cool prompt and just freeze up trying to figure out the ending before I even started. It felt like homework. Then, about six months ago, I read a tip from a writer on a blog. She said to just write the first 200 words of the scene the prompt gave you, and then stop. No plan, no ending. I tried it with a prompt about finding a key in a library book. I just wrote the character finding it and feeling the cold metal. I didn't know where it led. But having that little chunk written made me want to figure it out later, and the story actually got finished. It turned a big, scary task into a small, fun one. Has anyone else found a simple trick like that to get past the blank page?