Mildred lacks the insight that Clarisse possesses. While she is alive, Clarisse shares some of her insights with Montag:
"People don't talk about anything. They name a lot of cars or clothes or swimming pools mostly and say how swell! But they all say the same things and nobody says anything different from anyone else . . . My uncle says it was different once."
This insight into people, human motivation, and history is foreign to Mildred, who is content to exist in the present and with the superficial relationships that Clarisse had noticed in her observations.
When Beatty shows up to explain a few things about the history of books and why they needed to be eliminated, Montag has the courage to ask about Clarisse. Beatty says that Clarisse's crime initiated in wanting to know why things happen when she should have just been content to know how they happen.
Following Beatty's lengthy explanation about why it's necessary to limit the average person's access to information, Montag "sat, as if the house were collapsing about him and he could not move." Mildred simply disappears and returns back to her parlor with her "family." When her husband tells her that he isn't happy with their society, she replies, "I am. And proud of it." And when he tells her that he needs to do something, silently reflecting on his conversations with Clarisse and the life and ideas that died with her, Mildred replies, "I'm tired of listening to this junk."
Mildred doesn't have a sense of compassion. She doesn't have a sense of wonder or the desire to question the world around her. She is the model citizen the government has created, and she acts as they expect her to. By removing the true experience that is life from citizens, the government in Fahrenheit 451 creates people like Millie who are incapable of empathy.