Deep work is sustained, distraction-free concentration on cognitively demanding tasks — writing, analysis, strategic thinking, complex problem-solving. It is hard in an open-plan office because two compounding distraction sources make it structurally difficult: digital interruptions (notifications, checking habits) that trigger the brain’s orienting response, and acoustic distraction (intelligible background speech) that activates the phonological loop’s Irrelevant Speech Effect (ISE). Unlike personal distraction resistance, which can be partially addressed through habits and norms, the ISE is an involuntary cognitive mechanism that cannot be overcome through discipline — it requires physical acoustic isolation to DS,A ≥ 25 dB (ISO 23351-1) to be eliminated.