What does the phrase 'strikes a nail over the lines of destiny' mean in Chapter 10?

In Chapter 10 of the Shri Sai Satcharitra, the phrase "strikes a nail over the lines of destiny" is used to describe the profound power of the Sadguru to alter a devotee's fate. The chapter asserts that by placing unwavering faith in the Guru's feet, one's predetermined destiny can be fundamentally changed for the better. This concept is presented as a key benefit of devotion, alongside the idea that the Guru is the one eternal God who can guide a follower across the ocean of worldly existence. This power over destiny, as described in Chapter 10, is a testament to the Guru's supreme role in a devotee's spiritual and material life.