After being so disappointed by Baba's written reply, what prompted Damu Anna to travel to Shirdi?

Although Damu Anna was initially very crestfallen, the letter he received contained a crucial hint that inspired his journey. Chapter 25 explains that the reply letter, following Madhavrao's suggestion, also stated: 'There is a difference between hearing and seeing; you should come here in person.' This message sparked a new line of thought for Damu Anna. He felt it was right to go and held onto a glimmer of hope that a personal visit might yield a different outcome. He thought to himself, 'Who knows, there might be benefit in that too. Perhaps He will give permission.' This hope of potentially getting Baba's approval in person is what prompted him to travel to Shirdi.