What is ironic about mildreds statement that “i understand that one”

The irony is that, based on what we know about Mildred, she does not understand herself.

Explanation:

Fahrenheit 451 is a dystopian novel by Ray Bradbury about a future American society, where books are forbidden.

The main character in the story, Mildred, is obsessed with television and avoids confronting her life. She even attempted to kill herself by overdosing on sleeping pills. She is obviously suffering.

In part two, Montag encourages her to read some books that he managed to steal. Montag opens a book and reads the following line - 'That favorite subject, Myself.' Mildred replies "I understand that one." The irony in her reply is that she obviously does not understand herself. If she understood her feelings, she would have done something about them.