If I understand your question correctly, you're looking for someone to help you answer this tough question when you are interviewing for a new job. I find the best response to be a positive and upbeat one that emphasizes my skills and experience. For example, "While I enjoy the challenges of my current position, I see that the position you're seeking to fill has a broader scope of responsibilities and since my 5-year goal is to work into a management position, the opportunity to supervise a staff of three would be a welcome opportunity." Or if management is not something you're interested in, you could focus on other differences in the job tasks for the new position: more face-to-face contact with customers, more challenging day-to-day tasks. The key is to focus on a *positive* difference between your current job and the one for which you are applying.