Show that you can deal with disappointment and move on positively. Don't just tell them you handled the disappointment well; describe to them how you did it. Select a situation from your professional life where someone or something fell short of expectations and explain how you handled it. Also, describe what you learned and how you would approach the situation in the future. Avoid bragging or saying anything overly negative.

"My biggest professional disappointment occurred early in my career. After graduating from college, I pursued a role as a junior project manager in a local government water conservation role. I was excited to get started and situate myself as a professional in the field. Unfortunately, I struggled a lot throughout my first year in that position because I didn't believe in the work I was doing. Politics played a big role, and it took forever to get anything done. It was disappointing because, throughout college, I thought working for a government agency would be the right path for me. I decided to try something new and take on an internship in the private sector, which turned out to be a better fit."