1. Is it your story to tell? Do you care enough about the subject and the characters? “Write what you know” probably means choose things which matter a lot to you. Things you have a stake in.
2. Is it too personal? Some experiences are too close to us. We haven’t processed the deep emotions enough to put it into perspective for a reader. (Example: loved one killed by drunk driver.)
3. Is it going somewhere? Ask yourself if you can dramatize the idea in a series of scenes. Does it have a plot, is it going somewhere?
4. What’s at stake? How can you show rather than tell why it is so important the character? (Can you render your idea in scenes?)