In Chapter 37, Enzo is diagnosed with 'degenerative arthritis caused by hip dysplasia.' He finds that his movements are no longer smooth and easy, and he surmises that the diagnosis foreshadows the beginning of a journey that will ultimately lead to his demise.
With my diagnosis, I knew, would come my end. Slowly, perhaps. Painfully, without a doubt; marked by the signposts laid out by the veterinarian. The visible becomes inevitable. The car goes where the eyes go.
Enzo is resigned to his fate, but more than anything, his fundamental goal is to be reborn as a man in his next life. In the story, Enzo believes that everyone is the master of his own destiny, and it is his destiny to be reborn as a human being.
...we are the creators of our own destiny. Be it through intention or ignorance, our successes and our failures have been brought on by none other than ourselves.
Enzo's chronic condition worsens as the story concludes, but he is unperturbed because he is more than ready to relinquish his canine existence on earth. Both his mortal and immortal eyes are turned towards his goal. The visible (the long-looked for destiny) becomes inevitable and manifests itself when one's energies are focused on it. Hence, the 'car goes where the eyes go:' where the mind leads, the body will follow. Hope this helps!