Deep work is not a time management strategy — it is a neurological practice. The 23-minute re-engagement cost of a single interruption, the myelin development that deep cognitive work drives and shallow work does not, the variable dopamine reward schedule that trains compulsive distraction — understanding the biology is what separates engineers of deep work from those who merely attempt it. The complete neuroscience-based protocol for achieving and sustaining distraction-free cognitive states reliably and reproducibly.