the brothers mysterious to each other

Mario, who cannot not be sincere, keeps asking the one question Hal will not answer, and finally names the reason: "You never say, is why." Hal's reply is tender and total evasion at once, converting his own constitutional inability to say what he feels into a shared mystery, an "unbridgeable difference" that puts the failure between them rather than in him. The gap runs right through the two people closest in the house.