Why is Uncle John so unhappy?

The emotional pain people carry can often be masked. Some will withdraw into themselves, others will lash out; still others will turn to a crutch, such as liquor, as a poultice for pain. Sometimes, the wound is very deep. For Uncle John, his distress is so great that he protects himself in all of these ways: by being solitary, by drinking, and by developing an exterior so tough that he can never be hurt again.
For many years, John has kept to himself, even though his extended family lives relatively close by. When Tom returns home and learns from Muley that the family has gone to stay with John for a time, Tom expresses surprise:
"Damn' if I know how they're all sleepin' at Uncle John's. He on'y got one room an' a cookin' leanto, an' a little bit of a barn. Must be a mob there now."
As Tom and Casy discuss where and why the family has traveled the eight miles to John’s small home, Casy inquires about John:
“Just a lone man, ain't he? I don't recollect much about him.”
Tom replies:
Lonest goddamn man in the world," said Joad. "Crazy kind of son-of-a-bitch, too—somepin like Muley, on'y worse in some ways. Might see 'im anywheres—at Shawnee, drunk, or visitin' a widow twenty miles away, or workin' his place with a lantern.
Soon, it is revealed what has happened to Tom’s uncle to make him so unhappy. When John’s wife was four months pregnant when she complained to her husband of being in pain. Doctors, of course, cost money. John decided to wait it out and hope the pain got better. It did not and his wife died during the night.
John never forgave himself. Until this happened, Tom recalls, Uncle John had been an “easy-goin’ fella.” But the guilt of his negligence haunted him. For two years, the man “walks aroun' like he don't see nothin' an' he prays some...an' then he ain't the same. Sort of wild.” When any of his many nieces and nephews fell ill, John sent for the doctor, until Tom Senior told his brother to stop it. John complied, whether due to his brother’s admonition or a lack of money or both. But his guilt did not subside. For years after his wife’s death, John tried to make up for his “sin” with small acts of kindness. “Give away about ever'thing he got, an' still he ain't very happy," Tom tells Casy.
Uncle John’s story recounts an individual experience. Just as Steinbeck focuses in on the Joads and out on the larger similarly-suffering population, John’s story is a reminder of Plato’s admonition: “Be kind to everyone you meet for everyone is fighting a harder battle.”