Self-regulation disorders—substance addiction, compulsivity spectrum conditions, ADHD, and thought/mood disorders—share a common phenotype: the inability to constrain ongoing behaviour despite insight, consequences, or competing goals. We propose this reflects a shared mechanism: dysfunction of the astrocytic "grammar layer" at the neurovascular interface in prefrontal and striatal control circuits. Across ten conditions we find a recurring four-column pattern: behavioural constraint failure, astrocyte dysfunction, neurovascular impairment, and symptom improvement with astrocyte-restoring interventions. The mechanism presents in four forms: exogenous damage, endogenous dysfunction, gradient undersupply, and structural degradation. Two immediately testable predictions are offered: (1) stimulant response in ADHD correlates better with perfusion change than dopamine transporter occupancy; (2) ketamine response in depression correlates better with astrocytic/perfusion markers than glutamatergic markers.