It's never easy to discuss mistakes or regrets with an interviewer. This question sounds more intimidating than it is. Avoid sharing a mistake with dire consequences or that would reflect poorly upon you. Share instances where you executed sound judgment and did everything you could to remedy the mistake and reduce its negative impact. Explain the valuable lessons you learned from it and how you applied them forward, ensuring you did not repeat the mistake. Every mistake is a growth opportunity. Show your interviewer that you didn't waste the opportunity. Keep your answer light and focus on how you handled the consequences. Share what you learned and how you have improved.