For generations, the arc of a life well-lived has pointed toward rest — toward the earned quiet of retirement, the laying down of burdens. Yet science is quietly revising that story, finding that the mind, much like the body, requires continued engagement to remain whole. Research into cognitive aging now suggests that mental stimulation, purposeful reflection, and the management of chronic stress may do more to preserve the brain than any pharmaceutical yet devised. The question being raised is not whether we deserve rest, but whether the rest we have imagined for ourselves is truly what the