An autobiographical account is offered of how the medical study of self (immunology) became a chapter in the philosophical study of human agency (from Nietzsche and Thoreau to Freud by way of Wittgenstein). Whether viewed scientifically or philosophically, several themes converge on the intractable instability of any notion of selfhood—epistemological or moral. How this problematic motivated an extended analysis of selfhood refracts the psychology of the author and his pursuit of philosophy as self‐knowledge.