What your interviewer is really trying to do with this question beyond identifying any major red flags is to gauge your self-awareness and honesty. So, "I can not meet a deadline to save my life" is not an option but neither is "Nothing! I'm perfect!" Strike a balance by thinking of something that you struggle with but that you're working to improve. For example, maybe you have never been strong at public speaking, but you have recently volunteered to run meetings to help you be more comfortable when addressing a crowd.