Phenomena known as cognitive biases, when applied to the details of a patient’s medical history, evidently steered the first attempts at diagnosis in the wrong direction. A 60-year-old man presented after 6 weeks of progressively worsening fevers, weight loss, malaise, night sweats, and confusion. Originally, the fevers were intermittent and low grade at 37.7°C (99.9°F). In the 2 weeks prior to presentation, they occurred daily, with temperatures rising to 39°C (102°F). The patient also reported mild headaches, a dry cough, and palpable lymphadenopathy in his axilla and neck.