The characters in Long Day's Journey are absolutely obsessed with thinking over the past and either feeling guilty about what they've done, or blaming someone else for all the problems they face. Once one of the children dies at a young age and the mother becomes addicted to morphine, everyone keeps worrying about whether they should have had another kid, who was responsible for the baby's death, why the mother became addicted to morphine, and generally how they or others have failed as good mothers, fathers, sons, and brothers.
James is basically incapable of subordinating his own obsessions to the desires of others. He makes a show of sentimentality and compassion, but in the end he can't look far beyond Numero Uno.
James's and Jamie's thinking is dominated by a causal logic that always includes blame. No action can occur that isn't someone's fault.
At the most basic level, Long Day's Journey Into Night is a play about people who are suffering. The characters have basically nothing to do, as the adult sons aren't working, the father is in his off-season, and the mother doesn't work at all. They tend to sit around, argue, and suffer the pain of old wounds and dark prospects for the future. One son has consumption to worry about, and the mother is addicted to morphine, but these problems radiate to the father and other son as well, as they suffer from the consequences too. Everyone's bogged down in depressive thinking about the way things used to be (either good or bad) and their (probably awful) future.
The kind of suffering we see on this one day's journey into night doesn't appear to be much more serious than the suffering that's probably been going on in the Tyrone family every day for at least 20 years.
Instead of criticizing her means of coping with pain, the Tyrones ought to look into a less extreme way of dealing with Mary's arthritis. Mary has a legitimately painful disease that is the impetus for her use of morphine, as her physical pain combines with the knotty reminders of her loss of youth, innocence, and beauty to send her into a tailspin.
In Long Day's Journey Into Night, the Tyrone family's past and present have been so dire that normal coping mechanisms (family love, togetherness, etc.) can't keep up. So what do they turn to for relief? Alcohol and drugs. These forms of retreat might numb the pain, but they also bring their own problems – Mary's constant zoning out and Jamie's inability to hold down a job, to name two examples. There's also a vicious cycle involved in all of this: Mary takes drugs and the Tyrone men drink to escape, but they also feel bad about doing so, leading them to snipe at one another even more maliciously.
Despite all of his nostalgia for his Irish immigrant roots, James's choice of alcohol demonstrates exactly how much he has adopted wealthy American habits.
Jamie shows just as much dependence on women as he does on alcohol.
Everyone in Long Day's Journey into Night has some major anxiety about the lost Good Old Days and about old mistakes that still show scars. Both parents express real regret over choices they made in their youth: James wishes he could have been a more diverse actor and Mary seems to wish she had never married James. She is also absolutely haunted by the death of one of her children, and clearly feels guilt over it.
O'Neill switched his name with that of his deceased brother Edmund partly to ensure that the play isn't taken as literal autobiography, but also as a way of giving his brother a life on paper that he never had in real life.
The continual literary allusions provide another way for the Tyrones to avoid confronting current reality.
One way you could chart the trajectory of Long Day's Journey Into Night is to follow how willing the characters are to be honest with one another. As the play starts, everyone except for the eldest son is terrified of bringing up taboo subjects like drugs, alcohol, careers, and the past. When Jamie does bring them up (as he does so often), he's shot down by the rest of the family (twice with a blow to the face). Only by the end of the play, when the rules don't seem to matter any more, do the characters actually speak their minds.
The lies in this play aren't new, off-the-cuff, improvised lies; instead, they have been repeated often enough to be a comfort to the characters who cling to them.
The frequency with which body language and body types betrays the truth behind a bit of dialogue is evidence of a broader theme, throughout the play, of meaning residing primarily in organic, natural expression and environments.
One of the basic tensions underlying Long Day's Journey is the conflict between fate and free will. All the characters want to change their lives, but at the same time, they can't get this depressing fatalism out of their heads. The play's matriarch sums it up well when she says, "None of us can help the things life has done to us. They're done before you realize it, and once they're done they make you do other things" (2.1.76). We should point out that the idea of fate is different here than in a Greek tragedy. The characters aren't pawns of the gods. In Long Day's Journey Into Night, the word "fate" is short hand for family history and past mistakes. Each character struggles against the tides of the past. Even though they aren't battling divine will, they are all in least in some way shaped by forces that are out of their control.
In conjunction with her efforts to dull her pain with morphine, Mary resorts to a fatalist, inflexible philosophy of life that allows her to write off any blame she would otherwise assign to herself or others.
All of the philosophizing and book learning that has preoccupied Edmund has only made him more inept in practical matters.
The Tyrone family has no strong parent figure to take responsibility for the care of its members. Without supportive parents, the children are left to look after themselves and their parents, and they're simply not cut out for the responsibility.
Psychologists might say none of the Tyrones has a good support network. The father acts childishly most of the time, and the eldest son, at least, doesn't look up to him. This son, Jamie, is the character who requires the least caretaking, but that's really because both he and his parents think he's a lost cause. The younger son Edmund, meanwhile, is the sickly baby of the family. He's clearly the parents' favorite and can't seem to put his adult life in order. If you're looking for helpless characters, though, his mother gives Edmund a run for his money – she has to be coddled and protected from herself and the family's anger.
There's a weird vacuum, then, at the top of this family, with no respected leader and lots of people who demand help and care. The failure to take familial responsibility is a real problem in Long Day's Journey, as none of the characters has anyone they feel they can turn to in times of need.
Cathleen is as much a member of the family as Jamie, and certainly more instrumental to its (limited) stability.
This theme is a little more subtle, but with all of this American dream stuff, you can see that class and money matter in Long Day's Journey Into Night. The dad has done well financially, and he finds Socialism distasteful. As James points out, he learned the value of a dollar the hard way as a child, and his greatest fear is role people taking advantage of his wealth and cheating him. As a result, he has a hard time spending money, even on worthwhile causes, like quality healthcare for the family.
The family has two full-time helpers, and the mother's attitude toward them is telling. She thinks one is positively subhuman, but she's willing to use the other as a surrogate friend when she gets really lonely. The relationship isn't really one of friendship from the mother's end though – she's more looking for anyone who'll listen.
Through their frequent dehumanization, Cathleen and Bridget reveal the Tyrones' failure to separate themselves meaningfully from the wealthy families with whom they don't want to associate (such as the Chatfields and Harker).