After Emily dies and George throws himself on her grave, what is Emily referring to when she says that George and the other live people don't understand?

.Emily tells her that life for George will never be the same without her, adding, “Live people don’t understand, do they?”

.......Observing the funeral company, she says she never realized in life how troubled many people are. Nevertheless, she expresses a wish to return to life for a little while. Mrs. Gibbs says she can but advises her not to. So does Mrs. Soames. But Emily says she plans to return to a happy day, not a sad one. “Why should that be painful?”

A funeral party enters with a casket. Among the mourners are George, Dr. Gibbs, and the Webbs. While the living characters huddle at the back of the stage, Mrs. Soames and Mrs. Gibbs talk dispassionately about the cause of Emily’s death. Mrs. Soames reminisces about George and Emily’s wedding. A group standing by the grave begins singing “Blessed Be the Tie That Binds.” Emily emerges from the funeral party and joins the characters in the cemetery—her body has just been interred. She sits in an empty chair beside Mrs. Gibbs and tells her mother-in-law all about the improvements she and George had been making to their farm. Emily suddenly stops, seemingly struck by an epiphany, and looks at Mrs. Gibbs. “Live people don’t understand,” Emily says. Sitting with the dead, now one of them herself, Emily remarks how distant she feels from the living.

Even so, Emily says, she still feels like one of the living, and against the advice of the other dead souls, she decides to go back and relive one happy day from her life. With the assistance of the Stage Manager, Emily goes back to 1899, to the day of her twelfth birthday.

The sorrowful, emotional atmosphere of Act III stems not from Emily’s death, but from the realization that most people do not cherish life the way they should. Ironically, according to Emily’s experience during her flashback, the living despair about the end of life, but do not make much effort to cherish life while they still have it. Emily, however, is only able to realize how precious her life is after she has died. Even the dead characters who insist that Emily should not relive her life do so because it seems they once made the same attempt to return themselves. The dead already have made the painful realization that Emily will soon reach. Wilder reveals to his living audience that most people “don’t understand” that the power of life exists not only in the moments of great passion and joy, but in the details of everyday existence as well. When George prostrates himself on Emily’s grave at the end of the play, the dead react as if the time for emotion has passed.