The interviewer wants to understand the underlying motivations you have for your career selection to find out how committed you are to being a personal care aide and how good of a fit it is for you. They'll also want to find out if their values are your values. Try to demonstrate how you approach things or how your experience made a difference to patients and their families. Give a constructive response showing how well you can adapt and be able to cite situations or give specific examples that help prove your points. Make sure you're portraying positive attributes and characteristics, ones that can translate to this new position and add worth.