In my opinion, what makes Shaw's characters "life-like" is their fallibility. From the lesser to the major characters, all experience some sort of growth that makes them believeable, not just characters on a page.
Liza exhibits "lifelike-ness" in her ability to grow. She is not a static character. Although she comes to Higgins as a street-wise young girl who doesn't know a thing about the his elite world, she is intelligent and a fast learner. These innate traits help Liza ultimately understand that "the difference between a lady and a flower girl is not how she behaves, but how she's treated."
Higgins, however, isflawed from the beginning. He does not grow much. His fallibilty is his seeming lack of ability to treat everyone as real people, not lab specimens. He is beliveable, however, in that many people fail to see those who are not in their social class as their equals in any way.
Mrs. Pearce exhibits more growththan does her employer, Mr. Higgins. Although she initially is appalled by Liza, she soon becomes her champion, recognizing her own shortcomings and helps Liza throughout the play, often standing up for her to Henry.
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