The death of his father was unmistakably an ample moment of his teenage life, he had no way of expecting that outcome. He may not know it but lying is also his way of coping. Unlike with his mother, James was very close to his father. The understood each other and James showed this with a joke:
“’There’s a bear outside,’ said Tom intently.” Without his father’s usual creativeness around anymore it’s as if he’s taken it upon himself to replace him. It’s not like his mother would joke around with him. “We all loved puns except Mother, who didn’t get them.” In a way it is beneficial for him as it is a way to grieve his father’s death but his mother is right about one thing. It is that he is “cheating himself”. Rather than mourning it like normal people, he did not shed one tear at his father’s funeral, instead it was directed to his habit of lying. He may not realize it but in the end, he really is just fooling