What mistake did Babasaheb Tarkhad make while his son was away, and how did he come to realize it?

While his son was in Shirdi, Babasaheb Tarkhad made a mistake in the daily worship he had promised to perform. As Chapter 9 recounts, one day he was preoccupied with his business matters and, in his hurry, forgot to offer the customary piece of sugar candy as Naivedya to Sai Baba's photograph. He only realized his oversight later in the day when he sat down for his meal. It was his daily practice to consume the offered sugar candy as Prasad with his food. When the cook did not serve the Prasad on his plate as usual, he was immediately struck with remorse, understanding that the morning offering had been missed.