It's kind to avoid hurting other people's feelings.
Julie's sister asks her if Julie thinks her sister is an attractive girl.
Julie wants to answer her sister.
Julie tells her sister that she's attractive enough and besides that has a nice personality.
Julie tells her sister that she was born unlucky and that she just isn't attractive at all.
Julie's sister feels more confidence after hearing Julie's complimentary answer.
Julie's sister is emotionally devastated by Julie's comment and her self-esteem suffers.