What do I say about why I left my last job? - 8 months and counting

They always ask why I left, and I freeze. There are 9 people counting on me, so I am trying to be careful. I also do not want to seem like a risk. What do you say?

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.

Practise it out loud with a friend. Mine felt natural after the third try.