I know from my experience of delivering training programs and seminars on improving confidence and self esteem, that when participants are asked to state just five of their best qualities a hushed embarrassment fills the room. "I don't know," is the most common response.
Conversely, we're all a lot better at listing our faults and failings and can get onto that task without any difficulty! It's like most of us haven't even dared to think about the question, "What's good about me?" - if that's you, then it's even more important that you read on.