The interviewer is curious about what your circumstance might reveal about you as a potential employee. It's okay to be honest, but take care not to over share. Quitting your job before lining up another speaks to your poor planning skills. Being laid off or let go can present as a red flag if not presented in the appropriate context. If it's an employees' job market and you are testing the field, they'll undoubtably question your level of commitment to your current employer. Best to primarily focus on your wish list vs. career stagnation. Focus on the positives with a mindset for career growth. Steer away from speaking about your current or previous employers negatively. Be sincere, but frame your answer with a positive growth mindset.