Here then is repetition's double nature: it names both an endlessly predictable recurrence (the relentless crawl to infinity that is the experience of boredom, for example; or the equally unreachable horizon of obsession) and a ceaselessly renewable starting-point (the repetition that results from forgetting: at its most extreme, a neurological catastrophe that plunges the brain-damaged or demented patient into a lifetime of repetition).

Eternal Return Brian Dillon on the philosophy of repetition

Wiederholung und Differenz Gilles Deleuze und die Künste