All My Sons features a complex, fraying marital relationship between Kate and Joe Keller. Kate’s inability to accept her son’s death has left her mentally unstable. Trying to function while in a state of complete denial, Kate grasps at straws that she hopes will support her belief that Larry is Missing in Action (MIA) rather than dead. Joe seems to be in a different kind of denial, as he does not accept the extent to which his wife’s mental health has deteriorated. Arthur Miller carefully structured the play so as to reveal bits of important information at numerous points. The audience learns that Joe is in denial about more than Larry. He does not face up to his responsibility for the faulty parts. It turns out that displacing blame onto others is one of his severe character flaws; another is lying.

When Kate is forced to admit her husband’s errors and cover-ups, it is because her honesty helps reveal them. She tries to pretend she was mistaken about Joe’s health, but clearly as a wife, she would not forget if he had pneumonia. Her dramatic break from her husband occurs as she argues with Chris, even slapping him in the face. Kate reveals that she knows the truth in the way that she denies it: “Your brother's alive, darling, because if he's dead, your father killed him.” Early the next morning when they are alone, she tells her husband “You can't bull yourself through this one, Joe, you better be smart now.”

Ironically, up to that point in the play, Kate had seemed the fragile one. Miller ultimately reveals that Joe was also in a precarious state, as he is the one who takes his own life. With the revelation of Larry’s letter, Kate had finally accepted that he was gone. As the play ends, she tells Chris that he must forward with life.