What is the significance of the scene with Cantú's uncle in The Line Becomes a River?

When Cantú's uncle asks him how his job as a border patrol agent is going, he doesn't quite know what to say. He wants to tell him how he can barely sleep, how his mind is so full of violence that he can no longer perceive the beauty around him in the desert; he wants to tell his uncle that there's nothing for him in the borderland deserts and that he will find no peace there. But he doesn't. Instead, he just takes a deep breath, looks over at the water held back by the sagging dam, and tells his uncle that is job is good and that it's nice to be out in the desert away from the office for a change.
What this scene shows us is Cantú's shame and embarrassment at being a border patrol agent. The job is eating away at his soul yet he can't confide in his uncle about what it's doing to him, the immense psychological damage it's causing. Cantú's not proud of his work and the negative impact it's having on his physical and mental health, so he lies to his uncle as he doesn't want him to fret.