The nurse is breaking the principle of confidentiality by discussing a patient's condition in a public setting. Confidentiality is a fundamental ethical principle in healthcare that mandates healthcare professionals to protect patient information and only disclose it to authorized individuals involved in the patient's care. Violating this principle can lead to a loss of trust between the patient and healthcare provider, as well as potential legal repercussions. It is crucial for healthcare professionals to maintain patient privacy to uphold ethical standards and ensure the integrity of the healthcare system.