I have a few people in mind. I'll go ahead and choose Sakura. She is just the lowest self-esteemed person in this whole story. She's like i'm gonna do this, she goes and fails what she plans to complete. After she realized that Naruto or someone helps her out. She goes i'm a nobody, i'm weak, i'm useless, i couldn't do nothing, and i'll do better, but she fails again! She should be more positive self-image wise. If she would say, I will take this failed moment and make the next one even better that's much better. Instead of going through the same record of old words.