What specific event caused the narrator to doubt the value of visiting Sai Baba in Shirdi?

The narrator's interest in visiting Sai Baba was severely diminished by a tragic event that befell a close friend. As detailed in Chapter 2, this friend, who was the son of a Guru, lost his only healthy and virtuous son to a sudden fever. Despite trying all human remedies and even having the Guru sit by the child's side, the boy passed away. This incident led the narrator to question the very purpose of a Guru, making him think, "Is this the utility of a Guru? He couldn't even save an only son!" This profound disillusionment and the seeming powerlessness of a Guru against fate directly caused his enthusiasm for the Shirdi trip to go slack.