As it turned out, Sonny had some appealing characteristics. In the Gospel account, we find him out working in his father's fields, right up till suppertime. He was an industrious young man, laboring for the success of the family business. He was conscientious and dutiful. He might have given some thought at some time or another about striking out on his own.
Every boy does.
But his duty to father and family won out and he remained to do what was expected of him. But he was virtuous enough to be able to claim that he was righteous to his father without Dad laughing at him. But then nobody ever laughed too much at anything Sonny said. After all, Junior was the one that got the laughs. I wonder what would have happened had Junior met Sonny on the road instead of their father.