Anchoring bias is often considered the Achilles' heel of diagnostic reasoning. It's as though our brains close ranks around our first impression, then refuse to consider anything else. Once a patient is "billed" as a heart attack, or gastroenteritis, or anxiety, we view every data point through that particular lens. If the data doesn't fit, we tend to assume that it's merely because the illness is presenting atypically rather than that our diagnosis might be wrong or incomplete. Anchoring bias casts an even longer shadow in today's shift-oriented medical world, in which patients are serially handed off from one team to another. The label that is attached to them takes on a life of its own.