What was Sai Baba's personal experience with his Guru that taught him about perseverance and devotion?

Sai Baba recounts his profound experience in Chapter 19, explaining that he served at his Guru's feet for twelve years, a testament to his immense perseverance. He describes a state of complete and unwavering devotion, where he would gaze at his Guru's face day and night, feeling neither hunger nor thirst. His mind knew no other goal or meditation besides his Guru. This single-minded focus, Baba explains, was all his Guru expected from him. In return, Baba received immense love and constant protection, describing his time with his Guru as a 'festival of joy,' which shows how his perseverance in devotion was met with profound grace.