I'm not sure if you are aware, but you have to approach prompting Fable slightly differently from a model like Opus.

It's important to include the reason aka the why of your task [1] in your prompt. You'll get more mileage if you verbalize your thought process when prompting Fable. Anthropic say you should think of Fable as a "thought partner".

1: https://platform.claude.com/docs/en/build-with-claude/prompt...

2: You might find some of the example prompts listed here useful https://x.com/trq212/status/2073100352921215386