Modern medicine possesses unprecedented ability to detect the upstream contributors to chronic disease, yet routinely confines care to downstream symptom management. This essay argues that the gap is no longer one of knowledge or technology, but of ethical framing. Drawing on established principles from medical ethics, maritime rescue law, and positive-duty jurisprudence, When Capability Creates Obligation advances a simple but demanding claim: once preventable harm can be reasonably identified, refusal to engage it is no longer ethically neutral. “Do no harm,” while necessary, is insufficient in a world where inaction itself produces foreseeable suffering. Using gastritis as a representative case study, the essay examines how descriptive diagnoses become endpoints rather than signals, how symptom relief is mistaken for causal resolution, and how deferred responsibility accumulates as chronic disease and systemic overload. It challenges the circular defenses that justify this pattern—time scarcity, idiopathic labeling, and institutional constraint—and argues that contemporary data and computational tools have removed the excuse of invisibility. This is not a policy proposal or a technical manifesto. It is a moral clarification. Addressed to patients, clinicians, and the healthcare system alike, the essay contends that capability creates obligation—and that medicine must decide whether it is willing to acknowledge the duties its knowledge now entails.*author's note: This essay reflects the author’s ethical analysis and does not constitute medical advice.