Comment by muzani
We ask this question in interviews too. One purpose is we want people who disagree and can handle this maturely. Everyone has negative experiences. People who don't have likely never tried anything difficult. But you have to be diplomatic about this.
Practice it. Write the answer. Go over it for 20 hours. Treat it like a presentation because it is. I go so far as to make an AI "interviewer" in Vapi so I can voice it out, and you can mod the tone to be supportive, indifferent, sarcastic, etc.
If you're disappointed with yourself, say that. Humans make mistakes. Someone out there started smoking or drinking once. Someone had an affair. You don't know which of your interviewers did which, but you can assume that everyone has done something they knew was a bad idea.
It's also reasonable to assume that an applicant is leaving for reasons. Bored? Wants more money? That's a pretty bad reason. Unhappy? That's a much better reason. What's the catch? Why is this property on the market for cheap? A trick is to imply what people want to hear - you're looking to work with smarter people, better processes, get your shit together, etc.