What was the reason for Dev's failure to recognize Baba in the guise of the Sanyasi?

Dev's failure to recognize Baba was due to a prior encounter that clouded his perception. As Dev himself reflected in Chapter 40, the man who appeared as the Sanyasi had previously visited him to collect funds for cow protection. This meeting occurred before Dev had even extended the Udyapan invitation to Baba in Shirdi. Because of this, Dev's mind had already categorized the Sanyasi as a fundraiser. When this same person appeared for the meal, Dev's vision was confused by this preconceived notion, and he couldn't see past the disguise to recognize his Guru. He lamented that if the Sanyasi had appeared for the first time after the invitation, his perception might not have been so deluded.