Aristotle isn't simply saying that thinking hard keeps us alive—he's proposing that the *vitality* itself comes from mental exertion, not from mere physical existence. A person can breathe and eat for decades while mentally dormant, yet possess little of what Aristotle would recognize as life's essence. Consider someone who stops learning after thirty, who avoids difficult questions and settles into routine: by this standard, they've already begun a kind of decline, regardless of their heartbeat. The insight cuts against our modern comfort with passive contentment, suggesting that what makes life worth living is the active engagement of the mind.