Across the world, tens of millions of people live with dementia, and for decades the condition has felt like an inevitable shadow over aging. Yet the World Health Organisation now offers a measured but meaningful counterpoint: nearly half of all dementia risk is shaped not by fate, but by the accumulated choices of daily life. From blood pressure management to hearing care, from movement to human connection, the science suggests that the brain is more responsive to how we live than we once believed. This is not a promise of immunity, but an invitation to agency.