Sontag's redefinition of seriousness cuts against the grain of a common misunderstanding—that being serious means being solemn, rigid, perhaps even joyless. What she's really asking for is presence: the kind of alert engagement you see in someone truly absorbed in conversation, or in a parent's face when their child first speaks. The passionate person isn't necessarily the loudest; they're the one whose attention doesn't waver, whose stakes feel genuine because they haven't erected walls between themselves and the matter at hand. That's why a scientist can be as serious as a grieving widow, a child playing chess as serious as a surgeon—the seriousness lives in the quality of attention, not the subject matter.