Mary Tyrone's obsession with her past ruined her present.Commentplz answer in detail
In Eugene O'Neill's Long Day's Journey into Night, Mary Tyrone cannot find happiness in the present because she is emotionally stuck in the past. She constantly thinks about her girlhood, before she met James Tyrone, and wonders whether her life would have turned out differently had she never met him. Her life was simpler then. She lived in the convent and was happy there. She was also becoming a skilled pianist. Now, with an alcoholic husband who has not provided her with the home-life she expected, two alcoholic sons who both turned out to be disappointments, as well as her own morphine addiction, it is easy to see that she will never be able to return to those past, idyllic days.