How do we see the theme of fate in Appointment in Samarra?

The theme of fate is pretty common in John O’Hara’s debut novel, Appointment in Samarra. One important note is that the title of the book is borrowed from another story about fate (a man nearly dies while in Baghdad and flees to Samarra in an attempt to “cheat death,” only to re-encounter death upon arriving at his destination).
Julian’s predetermined fate shapes or dictates his self-destructive behaviors; suicide is part of his ancestry. His father, Dr. William Dilworth English, characterizes him as a weak-willed individual when he catches him stealing at a tender age:

And that was his reward: a son who turned out to be like his grandfather, a thief.

After this incident, Julian stops stealing, although his father is somewhat hesitant to believe so, primarily because he considers stealing to be in his blood. Julian’s wife also concedes that her husband’s doomed destiny is inevitable, which is quite evident when she claims that his time to die has come. Thus, we can term these incidents as the “shapers” of Julian’s destiny.

The title of the book introduces fate as a theme by referring to the old Mesopotamian tale of a man who confronts the inevitability of his own destiny. The man’s time to die has come, and he meets Death while trying to escape from her. Julian is like the man in this tale in that his journey is about the impossibility of avoiding a predetermined yet self-inflicted calamity. Julian’s grandfather committed suicide, and it is implied that this predisposes Julian to the same fate. After Julian decides to test the limits of what is socially acceptable within his privileged social group, he makes some attempts to repair his errors. Rather than fixing his missteps, he sinks deeper into a downward spiral that eventually takes him to the “appointment” spelled out in the book’s title: an appointment in Samarra equals an appointment with death. Despite the fact that Julian’s behavior angers his wife and isolates Julian from his group, none of his errors warrant his tragic decision. This reinforces the idea that Julian’s suicide had already been decided by fate.